Final 1.15 EOL Announcement

[dhawton]

Please provide a description for what this PR is for.

In preparation for next Tuesday's EOL date.

And to help us figure out who should review this PR, please
put an X in all the areas that this PR affects.

• Configuration Infrastructure
• Docs
• Installation
• Networking
• Performance and Scalability
• Policies and Telemetry
• Security
• Test and Release
• User Experience
• Developer Infrastructure

[ericvn]

This was included in the CVE docs.

[dhawton]

Now only updating the supported releases table which wasn't part of the CVE announcement PR.

[ericvn]

Thanks Daniel.

[istio-testing]

In response to a cherrypick label: #12919 failed to apply on top of branch "release-1.17":

Applying: Final 1.15 EOL Announcement
Using index info to reconstruct a base tree...
Falling back to patching base and 3-way merge...
CONFLICT (add/add): Merge conflict in content/en/news/support/announcing-1.15-eol-final/index.md
Auto-merging content/en/news/support/announcing-1.15-eol-final/index.md
error: Failed to merge in the changes.
hint: Use 'git am --show-current-patch=diff' to see the failed patch
Patch failed at 0001 Final 1.15 EOL Announcement
When you have resolved this problem, run "git am --continue".
If you prefer to skip this patch, run "git am --skip" instead.
To restore the original branch and stop patching, run "git am --abort".

[istio-testing]

In response to a cherrypick label: new issue created for failed cherrypick: #13006