feat: support kwargs for pg conn in pg_listener

[Alex-Izquierdo]

What:
This PR adds support for a dictionary of pg_param:value for the connection follow the standard use of Connection.connect with backward compatibility. Also enhances the validation of plugin arguments, extends test coverage and update module docstring according to the changes.

• New dict param postgres_params
• Check that dsn or postgres_params are defined
• Check required params (channels)
• Check the right type of all the arguments

Why:
Psycopg library has native support for a dsn string and kwargs params. There is no need to force the definition of a connection string, key:value pairs are more usual and makes easier the integration since it can be handled as a structured data.

This is also related to ansible/eda-server#1176 and part of a series of efforts to improve how we handle pg_notify configuration.

How:
Adding the new option postgres_params and making both, postgres_params and dsn optional but at least one must be provided. Encapsulates validation logic in _validate_args Psycopg library handles automatically the merge of both methods, we only need to pass the kwargs.