Apply shutdown timeout to http server to limit reload delay

[carsonip]

Motivation/summary

httpServer.stop may block indefinitely, potentially due to misbehaving connections.

Apply shutdown timeout to http server so that in a hot reload, the old and new server overlapping time is bounded.

Checklist

• Update CHANGELOG.asciidoc
• Documentation has been updated

For functional changes, consider:

• Is it observable through the addition of either logging or metrics?
• Is its use being published in telemetry to enable product improvement?
• Have system tests been added to avoid regression?

How to test these changes

May need to change the code to hang the http server to observe the shutdown timeout. Alternatively there may be a way to mock a misbehaving http client without code change.

Related issues

Part of #14337

[mergify]

This pull request does not have a backport label. Could you fix it @carsonip? 🙏
To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• backport-7.17 is the label to automatically backport to the 7.17 branch.
• backport-8./d is the label to automatically backport to the 8./d branch. /d is the digit.
• backport-8.x is the label to automatically backport to the 8.x branch.

[mergify]

backport-8.x has been added to help with the transition to the new branch 8.x.
If you don't need it please use backport-skip label.

[carsonip]

[to reviewer] Moving grpcServer.GracefulStop ahead of httpServer.stop, as this was how the code was originally written before elastic/gmux#13 was discovered. Now that it is fixed, we can revert it, so that it sends GOAWAY to grpc clients.

[mergify]

This pull request is now in conflicts. Could you fix it @carsonip? 🙏
To fixup this pull request, you can check out it locally. See documentation: https://help.github.com/articles/checking-out-pull-requests-locally/

git fetch upstream
git checkout -b limit-reload-delay upstream/limit-reload-delay
git merge upstream/main
git push upstream limit-reload-delay