Support changing CDC related configs dynamically

[overvenus]

Feature Request

Is your feature request related to a problem? Please describe:

Support changing CDC configs dynamically via SQL. https://docs.pingcap.com/tidb/stable/dynamic-config

Example:

tikv/components/server/src/server.rs

Lines 759 to 762 in 3f0c72a

	cfg_controller.register(
	tikv::config::Module::Raftstore,
	Box::new(RaftstoreConfigManager(raft_store)),
	);

TiCDC also need a config manager to update its config.

[overvenus]

PTAL @hi-rustin

[Rustin170506]

/assign

I will take a look.

[Rustin170506]

/difficulty medium