[Internal] Add CustomizableSchema for Plugin Framework (#3927)

## Changes
<!-- Summary of your changes that are easy to understand -->
- Addressed comments in
#3880
- Add CustomizableSchema for PluginFramework

## Tests
<!-- 
How is this tested? Please see the checklist below and also describe any
other relevant tests
-->

- [x] `make test` run locally
- [x] relevant change in `docs/` folder
- [x] covered with integration tests in `internal/acceptance`
- [x] relevant acceptance tests are passing
- [x] using Go SDK

internal/pluginframework/tfschema/customizable_schema.go

@@ -0,0 +1,154 @@
+package tfschema
+
+import (
+	"fmt"
+	"reflect"
+
+	"github.com/databricks/terraform-provider-databricks/common"
+	"github.com/hashicorp/terraform-plugin-framework/schema/validator"
+)
+
+// CustomizableSchema is a wrapper struct on top of AttributeBuilder that can be used to navigate through nested schema add customizations.
+type CustomizableSchema struct {
+	attr AttributeBuilder
+}
+
+// ConstructCustomizableSchema constructs a CustomizableSchema given a map from string to AttributeBuilder.
+func ConstructCustomizableSchema(attributes map[string]AttributeBuilder) *CustomizableSchema {
+	attr := AttributeBuilder(SingleNestedAttributeBuilder{Attributes: attributes})
+	return &CustomizableSchema{attr: attr}
+}
+
+// ToAttributeMap converts CustomizableSchema into a map from string to Attribute.
+func (s *CustomizableSchema) ToAttributeMap() map[string]AttributeBuilder {
+	return attributeToMap(&s.attr)
+}
+
+// attributeToMap converts AttributeBuilder into a map from string to AttributeBuilder.
+func attributeToMap(attr *AttributeBuilder) map[string]AttributeBuilder {
+	var m map[string]AttributeBuilder
+	switch attr := (*attr).(type) {
+	case SingleNestedAttributeBuilder:
+		m = attr.Attributes
+	case ListNestedAttributeBuilder:
+		m = attr.NestedObject.Attributes
+	case MapNestedAttributeBuilder:
+		m = attr.NestedObject.Attributes
+	default:
+		panic(fmt.Errorf("cannot convert to map, attribute is not nested"))
+	}
+
+	return m
+}
+
+func (s *CustomizableSchema) AddValidator(v any, path ...string) *CustomizableSchema {
+	cb := func(attr AttributeBuilder) AttributeBuilder {
+		switch a := attr.(type) {
+		case BoolAttributeBuilder:
+			return a.AddValidator(v.(validator.Bool))
+		case Float64AttributeBuilder:
+			return a.AddValidator(v.(validator.Float64))
+		case Int64AttributeBuilder:
+			return a.AddValidator(v.(validator.Int64))
+		case ListAttributeBuilder:
+			return a.AddValidator(v.(validator.List))
+		case ListNestedAttributeBuilder:
+			return a.AddValidator(v.(validator.List))
+		case MapAttributeBuilder:
+			return a.AddValidator(v.(validator.Map))
+		case MapNestedAttributeBuilder:
+			return a.AddValidator(v.(validator.Map))
+		case SingleNestedAttributeBuilder:
+			return a.AddValidator(v.(validator.Object))
+		case StringAttributeBuilder:
+			return a.AddValidator(v.(validator.String))
+		default:
+			panic(fmt.Errorf("cannot add validator, attribute builder type is invalid: %s. %s", reflect.TypeOf(attr).String(), common.TerraformBugErrorMessage))
+		}
+	}
+
+	navigateSchemaWithCallback(&s.attr, cb, path...)
+
+	return s
+}
+
+func (s *CustomizableSchema) SetOptional(path ...string) *CustomizableSchema {
+	cb := func(attr AttributeBuilder) AttributeBuilder {
+		return attr.SetOptional()
+	}
+
+	navigateSchemaWithCallback(&s.attr, cb, path...)
+
+	return s
+}
+
+func (s *CustomizableSchema) SetRequired(path ...string) *CustomizableSchema {
+	cb := func(attr AttributeBuilder) AttributeBuilder {
+		return attr.SetRequired()
+	}
+
+	navigateSchemaWithCallback(&s.attr, cb, path...)
+
+	return s
+}
+
+func (s *CustomizableSchema) SetSensitive(path ...string) *CustomizableSchema {
+	cb := func(attr AttributeBuilder) AttributeBuilder {
+		return attr.SetSensitive()
+	}
+
+	navigateSchemaWithCallback(&s.attr, cb, path...)
+	return s
+}
+
+func (s *CustomizableSchema) SetDeprecated(msg string, path ...string) *CustomizableSchema {
+	cb := func(attr AttributeBuilder) AttributeBuilder {
+		return attr.SetDeprecated(msg)
+	}
+
+	navigateSchemaWithCallback(&s.attr, cb, path...)
+
+	return s
+}
+
+func (s *CustomizableSchema) SetComputed(path ...string) *CustomizableSchema {
+	cb := func(attr AttributeBuilder) AttributeBuilder {
+		return attr.SetComputed()
+	}
+
+	navigateSchemaWithCallback(&s.attr, cb, path...)
+	return s
+}
+
+// SetReadOnly sets the schema to be read-only (i.e. computed, non-optional).
+// This should be used for fields that are not user-configurable but are returned
+// by the platform.
+func (s *CustomizableSchema) SetReadOnly(path ...string) *CustomizableSchema {
+	cb := func(attr AttributeBuilder) AttributeBuilder {
+		return attr.SetReadOnly()
+	}
+
+	navigateSchemaWithCallback(&s.attr, cb, path...)
+
+	return s
+}
+
+// navigateSchemaWithCallback navigates through schema attributes and executes callback on the target, panics if path does not exist or invalid.
+func navigateSchemaWithCallback(s *AttributeBuilder, cb func(AttributeBuilder) AttributeBuilder, path ...string) (AttributeBuilder, error) {
+	current_scm := s
+	for i, p := range path {
+		m := attributeToMap(current_scm)
+
+		v, ok := m[p]
+		if !ok {
+			return nil, fmt.Errorf("missing key %s", p)
+		}
+
+		if i == len(path)-1 {
+			m[p] = cb(v)
+			return m[p], nil
+		}
+		current_scm = &v
+	}
+	return nil, fmt.Errorf("path %v is incomplete", path)
+}