Support setting tcp keepalive duration

[evenyag]

What problem does the new feature solve?

Sometimes we may want to configure the TCP keepalive idle for a connection in the Postgres or MySQL handler of GreptimeDB

https://www.postgresql.org/docs/current/runtime-config-connection.html#RUNTIME-CONFIG-TCP-SETTINGS

It may be useful if we run the fronted after an LB so we can use the keepalive probe to keep the connection.

What's more, we may also find a way to configure the keepalive idle for the HTTP server since we can't set that in axum after #5417

What does the feature do?

Adds server side configurations for keepalive related options

Implementation challenges

We have the following different handlers to support

• MySQL Support setting tcp keepalive duration #5493
• PostgreSQL Support setting tcp keepalive duration #5493
• HTTP

It isn't easy to test in an integration test.