Is your feature request related to a problem? Please describe.
Support the IF NOT EXISTS keyword on CREATE SOURCE|SINK CONNECTOR. For example:

CREATE SOURCE CONNECTOR IF NOT EXISTS <connector> ...;
CREATE SINK CONNECTOR IF NOT EXISTS <connector> ...;

Describe the solution you'd like
Create the source/sink connector only if it does not exist.

**Describe alternatives you'

Currently, you are not able to use middleware per handler in "clean way" (you can still manually wrap the handler function, or have separated router).

It would be nice to be able to add middleware per handler.

As a good reference point, you can use chi router: https://github.com/go-chi/chi

我看到可以通过Prometheus搭建监控环境，如果有图文，更容易理解．