Release-3.5: server/etcdmain: add configurable cipher list to gRPC proxy listener

[dusk125]

This is a backport of #14308

[ahrtr]

Please fix the fmt & test error.

Usually we only backport bug fix to stable release, but exposing secure ciphers is a common and important part of any service, so It's OK to backport it.

[ahrtr]

Please also remove the CHANGELOG item from 3.6 and add a new item for changelog-3.5. FYI. #14476 (comment)

[dusk125]

Changelog PR here. Quick question, I'm planning on backporting this change to 3.4, should I just wait to update the changelog until I get that PR open, or should we go through this and #14524 and when I have the 3.4 PR just open another for moving the changelog item from 3.5 to 3.4?

[ahrtr]

1. It's OK to backport this PR to both 3.5 and 3.4 to me, but we still need other maintainers' approval.
2. Based on Changelog: add item into 3.6 for the fix on panic in readonly serializable txn #14476 (comment) , eventually we need to add changelog items for both 3.4 and 3.5.

[dusk125]

1. It's OK to backport this PR to both 3.5 and 3.4 to me, but we still need other maintainers' approval.
2. Based on Changelog: add item into 3.6 for the fix on panic in readonly serializable txn #14476 (comment) , eventually we need to add changelog items for both 3.4 and 3.5.

Sounds good, thanks!

[spzala]

lgtm. Re-running failed tests.

[ahrtr]

LGTM

Thanks both @dusk125 and @spzala