Integrate StartCommandHandler instead of forking server

I was recently integrating with `cosmos/evm` and I found unpractical that cosmos/evm was requiring a new server command instead of implementing the `StartCommandHandler`. This makes combining projects using the StartCommandHandler impossible without forking `cosmos/evm`:

https://github.com/cosmos/cosmos-sdk/blob/v0.50.14/server/start.go#L111-L131

I see that `cosmos/evm` has its own Application interface, but this can be solved by type casting inside the StartCommandHandler.
Flags can be added in `AddFlags`.

Integrating it would it more in-line with the SDK and reduce code duplication as well.

Start with the linked Cosmos SDK v0.50.14 server/start.go implementation of StartCommandHandler, then inspect cosmos/evm’s current server command and Application interface. Confirm how AddFlags should supply existing flags and how the application can be adapted without a fork. Done means cosmos/evm exposes the handler, preserves required flags and startup behavior, and can be composed by projects using the SDK handler.

Written by the indexing model from the issue text.