refactor(health): restructure health check implementations into dedicated check package

- Move health check implementations from monitor/ to new check/ package
- Add h2c, tcp4/6, udp4/6 scheme support to agent health check API
- Add timeout URL parameter to agent health check endpoint
- Remove unused agent dependencies (dnsproviders, lego, various cloud SDKs)
- Use net.JoinHostPort instead of fmt.Sprintf for port joining

internal/docker/client.go

@@ -250,7 +250,7 @@ func (c *SharedClient) Key() string {
 	return c.key
 }
 
-func (c *SharedClient) Address() string {
+func (c *SharedClient) DaemonHost() string {
 	return c.addr
 }