GetClientxxx functions should take the ClientID instead of the internal uuid ID

[adamwoolhether]

Describe the bug
The API to run GetClientxxx methods is unnecessarily clunky.

I realize this is not necessarily a bug, but i'm having trouble understanding logic behind the current implementation, which makes for an overly verbose operation, when considering that the "clientid" parameter is unique in KeyCloak.

To Reproduce
Try to get a client's secret with the Client ID:

creds, err := client.GetClientSecret(ctx.Background, token.AccessToken, "master", "my-client")
if err != nil {
	panic(err)
}

Expected behavior
This should return the client secret of the client with the client ID of "my-client"

Additional context
Instead, we have to first define a string, run GetClients with the pointer of the string, and then run GetClientSecret with a dereferenced pointer of the first index of the response from GetClients

clientName := "my-client"
c, err := client.GetClients(ctx, token.AccessToken, "master", gocloak.GetClientsParams{ClientID: &clientName})
if err != nil {
	panic(err)
}

creds, err := client.GetClientSecret(ctx, token.AccessToken, "master", *c[0].ID)
if err != nil {
	panic(err)
}