add timeout configs (ostracon#150)

[0Tech]

The subject of the triage:

• chore: config timeout and connection pool ostracon#150

[loloicci]

ostracon#150

• adds explicit settings of ReadTimeout and WriteTimeout in the rpc config
• adds IdleTimeout as a field of the rpc config

the former is not needed by lbm, but the latter is needed by lbm. whether does the original cometbft need it or not is under researching

[loloicci]

• we can suggest the former to the upstream, and it is an easy change. It looks good that our code and upstream's code are the same about this feature.
• we can suggest the latter to the upstream, but it is a kind of a breaking change and needs to change SDK to use it like https://github.com/search?q=repo%3AFinschia%2Ffinschia-sdk%20IdleTimeout&type=code.

We need to discuss whether we should suggest them.

[Mdaiki0730]

I thought it would be good to consider this issue in parallel with #37.
This is because the modifications and the purpose are almost the same.

Is config an option?
If the default value is used even if it is empty, I think it would be a good idea to issue a PR.

[loloicci]

Without this PR, IdolTimeout is always as same as ReadTimeout. If WriteTimeout is shorter than it, timeout problems may happen. So I will suggest it to upstream.