DOC-2498: Default values for tinycomments_author and tinycomments_author_name when empty string provided

[FarzadHayat]

Ticket: DOC-2498

Site: Staging branch Site: Known issue

Changes:

• fix for TINY-11323
• update 7.4 release notes - known issues

Pre-checks:

• [x] Branch prefixed with feature/<version>/, hotfix/<version>/, staging/<version>/, or release/<version>/.
• [-] modules/ROOT/nav.adoc has been updated (if applicable).
• [x] Included a release note entry for any New product features.
• [-] If this is a minor release, updated productminorversion in antora.yml and added new supported versions entry in modules/ROOT/partials/misc/supported-versions.adoc.

Review:

• [ ] Documentation Team Lead has reviewed