DOC-2409: update 6 docs support page to include 6.8 row and End of Community Support column

[FarzadHayat]

Ticket: DOC-2409

Site: Staging branch

Explanation: the new dates added here are the same as currently available on 7 Docs - Support Page up to and including v6.8.

Changes:

• DOC-2409: update 6 docs support page to include 6.8 row and End of Community Support column

Pre-checks:

• [x] Branch prefixed with feature/<version>/, hotfix/<version>/, staging/<version>/, or release/<version>/
• [-] modules/ROOT/nav.adoc has been updated (if applicable)
• [-] Files has been included where required (if applicable)
• [-] Files removed have been deleted, not just excluded from the build (if applicable)
• [-] Files added for New product features, and included a release note entry.

Review:

• [x] Documentation Team Lead has reviewed