Added the requested feature in PR 8132 and fixed the order issue

[Mujeeb4]

Reference Issues/PRs
Resolves sktime#8128
Replaces sktime#8132 (previous WIP PR)

What does this implement/fix? Explain your changes.
This PR adds module-based subsections to the changelog generator, as requested in issue sktime#8128.

The generator now automatically creates subsections within "Enhancements" and "Fixes" sections based on module tags in PR labels (like "module:forecasting" or "module:classification").

Key changes:

• Track module tags for each PR in assign_prs function
• Create a mapping dictionary from module tags to human-readable subsection titles
• Enhance render_changelog to group PRs by module within appropriate sections
• Use proper RST formatting for subsections (with ^ underlines)
• Fix handling of "benchmarking" and "base-framework" module tags that weren't being properly classified
• Ensure sections appear in the preferred order (Enhancements, Documentation, Maintenance, Fixes)
• Add support for user credits in PR titles (starting with &username)
• Format dependency version strings in dependabot PRs with double backticks

Does your contribution introduce a new dependency? If yes, which one?
No new dependencies are introduced.

What should a reviewer concentrate their feedback on?

• The PR addresses all the issues mentioned in [ENH] improve changelog generator to sort by subsection sktime/sktime#8128
• The implementation correctly groups PRs by module tag
• The output format follows the RST conventions used in previous changelogs

PR checklist

• The PR title starts with [ENH] for enhancement