Add check for go mod tidy

[Moulick]

Description of your changes

ref: crossplane-contrib/function-go-templating#105 (comment)

1. It looks like the go.sum is very bloated due to missing cleanup. All I have done is run go mod tidy to remove unused dependencies. This is generally a good practice and results in faster downloads/less cache.
2. Also added config to renovate to instruct it to do the go mod tidy whenever it upgrades a dependency.
3. Add a check in lint to catch future missing cleanup

I have:

• Read and followed Crossplane's contribution process.
• Run go test ./...
• Added or updated unit tests for my change.

[Moulick]

@jbw976 Here you go! Could you please approve running the pipeline 😄

[Moulick]

@jbw976 looks good to merge IMHO

[Moulick]

@jbw976 hey, anything holding this up?

[Moulick]

So looks like the go.mod has been cleaned up in some other PR. Can we merge this one soon so the GitHub Actions and Renovate config gets in?