Add dot release docs for server v11.10.2, v11.9.2, v11.7.11 (#38388)

* Add dot release docs for server v11.10.2, v11.9.2, v11.8.6, v11.7.11

Bump the latest release and ESR references across the deployment guides,
the server releases table, and the version archive (Enterprise and Team
Edition), and add changelog entries for each dot release.

SHA-256 checksums, release dates, severity levels, pre-packaged plugin
versions, and the release-specific fix bullets are left as TBD: these
releases are not yet tagged, so none of that is available to look up.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0131cCrZyHH1aNJbZK1sedZm

* Fill in changelog fixes and plugin versions for v11.10.2, v11.9.2, v11.8.6, v11.7.11

Derived the per-release bullets from the commits on release-11.10,
release-11.9, release-11.8 and release-11.7 since v11.10.1, v11.9.1,
v11.8.5 and v11.7.10 respectively.

Pre-packaged plugin versions come from the diff of PLUGIN_PACKAGES in
server/Makefile between each previous tag and its branch head. Fix
bullets use each PR's own release-note block where one exists, and reuse
the existing v11.10.1/v11.7.10 wording for the changes already described
there. CI-only, e2e-only and release-note-none changes are omitted, as
are the routine "Update latest patch version" commits.

No migrations changed on any of the four branches, so each entry keeps
the standard "contains no database or functional changes" line. Go
runtime versions are unchanged on all four branches, so no Go bullet.

Release dates, severity levels and the version-archive SHA-256 checksums
remain TBD: none of the four versions is tagged or published yet.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019ManuzLgwfsms5x8Uvc9Up

* Add mention keyword limits bullet to the v11.8.6 changelog entry

release-11.8 picked up #38121 (MM-70273) in #38349 after the entry was
written, so 11.8.6 now carries the same mention_keys validation already
listed under 11.7.11. Wording matches that entry and the PR's own
release note.

* Update mattermost-v11-changelog.mdx

* Update mattermost-v11-changelog.mdx

* Add changelog entries for fixes landed on the release branches since the draft

Sweep of release-11.10, release-11.9, release-11.8 and release-11.7 for
commits merged after each branch's dot-release version bump that were not
yet reflected in the changelog draft.

- v11.10.2, v11.9.2: mention_keys validation limits (MM-70273).
- v11.8.6: msgpack fork byte-string allocation cap (MM-70247).
- v11.7.11: outgoing OAuth client secret re-entry (MM-70208) and the
  FileInfo/Channels bulk-indexing query optimization (MM-70511).

Changes labelled Changelog/Not Needed on their source PR are deliberately
omitted: the missed go.mod Go bumps (#38102), the multibyte mention keyword
precompute (#38038), the release-11.7 dependency refresh (#38118) and
lodash-es bump (#38030), post type validation alignment (#38054), the
NewTransportForInternalConnections backports supporting MM-70507, and the
E2E/CI-only cherry-picks.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WqDQyXVPxnfFScXJWB16m4

* Update mattermost-v11-changelog.mdx

* Correct dot release changelog entries against the release branches

- v11.9.2: bump pre-packaged Agents plugin to v2.4.5, cherry-picked to
  release-11.9 in #38429 after this entry was written.
- v11.7.11: drop the idx_channels_create_at_id and idx_fileinfo_create_at_id
  database changes. #38206 split the index additions into a separate change,
  and migrations 000219/000220 are on master only, not release-11.7, which
  has gained no migrations since v11.7.10.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01T1gWC2qsWd9AtNFPRku9AE

* Update mattermost-v11-changelog.mdx

* Update mattermost-v11-changelog.mdx

* Drop v11.8.6 and move remaining releases to 2026-09-15

v11.8.6 is not shipping in this batch, so every reference to it is
reverted to the released v11.8.5.

- version-archive.mdx: both the Enterprise and Team Edition v11.8
  blocks are restored verbatim, which puts back the real v11.8.5
  SHA-256 checksums. Renaming the version string alone would have left
  the placeholder TBD checksums against an already-released build.
- mattermost-server-releases.mdx: the v11.8 row in the Latest releases
  table is restored, repointing the download and both SBOM links.
- mattermost-v11-changelog.mdx: the new v11.8.6 entry is removed
  rather than renamed, because the section already carries a v11.8.5
  entry and renaming would have produced a duplicate.

The v11.8 content in all three files is now byte-identical to the
base revision.

The three releases still in this batch move from 2026-09-11 to
2026-09-15: v11.10.2, v11.9.2, and v11.7.11.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Nrmq4ezefYWqa9YkxtX3mR

* Update version-archive.mdx

---------

Co-authored-by: Claude <noreply@anthropic.com>