[FEATURE] v4/sync/etcd - add username/password options

[dbereza-machinify]

Is your feature request related to a problem? Please describe.
Currently, the v4/sync/etcd plugin does not allow passing in a username/password for RBAC authentication with etcd, either embedded in the endpoint URL or as separate custom options.

Describe the solution you'd like
The etcd client library expects the username/password for RBAC authentication passed in the config, which is being defined here:

plugins/v4/sync/etcd/etcd.go

Lines 174 to 177 in 0ed40ba

	c, err := clientv3.New(clientv3.Config{
	Endpoints: endpoints,
	TLS: options.TLSConfig,
	})

Currently, the username / password are not being defined here, and embedding the username/password into the endpoint URL does not cause the etcd client to parse them out and use them for RBAC auth.

As such, the username/password could be parsed out of the sync.Nodes sync option, which isn't super ideal, or new etcd-specific credential options could be created and stored/retrieved from the option context.

Additional context
N/A

[xpunch]

plugins/v4/registry/etcd/options.go

Lines 20 to 27 in 9711876

	func Auth(username, password string) registry.Option {
	return func(o *registry.Options) {
	if o.Context == nil {
	o.Context = context.Background()
	}
	o.Context = context.WithValue(o.Context, authKey{}, &authCreds{Username: username, Password: password})
	}
	}

Hope this can be helpful.

[dbereza-machinify]

Yep yep, thanks!

I was hoping to use that same code once the Context option was added to the sync interface, for consistency :)