* rpc: Make HTTP server timeout values configurable

* rpc: Remove flags for setting HTTP Timeouts, configuring via .toml is sufficient.

* rpc: Replace separate constants with a single default struct.

* rpc: Update HTTP Server Read and Write Timeouts to 30s.

* rpc: Remove redundant NewDefaultHTTPTimeouts function.

* rpc: document HTTPTimeouts.

* rpc: sanitize timeout values for library use