chore(ci): add changelog automation

[vm-001]

Summary

Add changelog automation tool(implemented by GitHub workflow) to generate changelog file automatically based on the PR title.

PR title is not always qualified to be the changelog. For example, #11427 (feat(http-log): add allow list for logged headers), the user facing changelog should be more detailed by including the added fields.

message: "**HTTP-Log**: add `enable_logged_headers_allow_list` and `logged_headers_allow_list` fields in HTTP Log plugin."
type: feature
scope: Plugin
prs:
  - 11427

Therefore, I add a changelog form in PULL_REQUEST_TEMPLATE.md to allow contributors and reviewers to override it:

### Changelog

message:
type:
scope:
prs:
issues:

Once the changelog form is updated, people can easily re-generate changelog by leaving a comment( /update-changelog )

[vm-001]

#11514