Check Release Notes GitHub workflow

[igordmn]

Fixes https://youtrack.jetbrains.com/issue/CMP-7409/Add-a-CI-check-for-PR-containing-Release-Notes

• Add a GitHub workflow that checks Release Notes are correctly added. Runs automatically on creation and description change
• Move the guide into one file from the PR templates
• Parse categories for the script instead of hardcoding them (to have a single source of truth in the guide)
• Don't do network requests to avoid rate limit (60 requests per hour), read the description from the workflow variable

Also added to compose-multiplatform-core

Testing

1. Change Release Notes in this PR
2. CI successes with correct Release Notes
3. CI fails with incorrect ones

(Replace RR by R, otherwise the check picks a wrong section, I think no need to write additional logic just for this PR)

Correct N/A:

## RRelease Notes
N/A

Correct change:

## RRelease Notes
### Features - iOS
- Simple feature

Release notes missing:

Title is incorrect:

## RRelease Note
### Features - iOS
- Simple feature

Section isn't standard:

## RRelease Notes
### Features - Compose
- Simple feature

Items are missing:

## RRelease Notes
### Features - iOS

Sections are missing:

## RRelease Notes
- Simple feature

Testing

Tested for injections

1. For script injection

"; echo QQ > prDescription.txt #

2. For workflow injection

q
      run: |
        echo "QQ"

3. Verified that injection into changelog.main.kts isn't possible, as it doesn't execute anything parsed (including links)

Release Notes

N/A