Added deprecations page for Cohesivo 6.0

[mnocon]

Target: 5.0, 6.0

Adding deprecations page for the upcoming Cohesivo 6.0, to let Partners know about the upcoming changes ahead of time.

For now, the following changes are covered:

• IBX-11826: Cleaned up http-cache ResponseTagger deprecations http-cache#82 (http cache)
• IBX-11974: Added Rector rule migrating DeduplicateStamp to Contracts namespace rector#49 (new rule)
• Described stamps for Ibexa Messenger #3272 (messenger changes)

As a new Rector rule is added, there's a need for dedicated Rector page:

I've extracted the exsiting content (from update_to_5.0.md and package's README) into a separate page we can refer people to.

As this might be the first time people hear about Cohesivo, I've added 2 links explaining the business reasoning.

Status: this needs to be merged with the upcoming release, as this is when the Rector rule becomes available.

Link checker results should be ignored, there's a known issue here (fixed in #3280 )

[github-actions]

Preview of modified files

Preview of modified Markdown:

• docs/release_notes/cohesivo_v6.0_deprecations.md
• docs/resources/rector.md
• docs/resources/resources.md

[github-actions]

Summary

Status	Count
🔍 Total	761803
🔗 Unique	15043
✅ Successful	7277
⏳ Timeouts	0
🔀 Redirected	0
👻 Excluded	754523
❓ Unknown	0
🚫 Errors	3
⛔ Unsupported	0

Errors per input

Errors in site/release_notes/cohesivo_v6.0_deprecations/index.html

• [404] https://github.com/ibexa/documentation-developer/blob/5.0/docs/release_notes/cohesivo_v6.0_deprecations.md (at 194:10) | Rejected status code: 404 Not Found

Errors in site/resources/rector/index.html

• [404] https://github.com/ibexa/documentation-developer/blob/5.0/docs/resources/rector.md (at 196:10) | Rejected status code: 404 Not Found
• [404] https://github.com/ibexa/eslint-config-ibexa/blob/main/prettier.js (at 14488:77) | Rejected status code: 404 Not Found

Full Github Actions output