Cherry pick v5.0 -> 3.3

[mnocon]

Cherry-picks the initial set of changes from v5 to 3.3

The biggest obstacle is that the improved release notes pages were never backported to 3.3, hence I'm adding links to "Full release notes" here.

[github-actions[bot]]

Preview of modified Markdown:

• docs/getting_started/requirements.md
• docs/index.md
• docs/release_notes/ibexa_dxp_v4.6.md
• docs/release_notes/ibexa_dxp_v5.0.md
• docs/release_notes/ibexa_dxp_v5.0_deprecations.md
• docs/update_and_migration/from_4.6/update_to_5.0.md
• docs/update_and_migration/from_5.0/update_from_5.0.md
• docs/update_and_migration/update_ibexa_dxp.md