Add support for API key authentication with PMM

Our Operator comes with integration with Percona Monitoring and Management (PMM).

Right now the only possible way to authenticate with PMM server is with user and password. At the same time recommended way is to authenticate with API key.

See https://docs.percona.com/percona-monitoring-and-management/details/api.html#api-keys-and-authentication

This Improvement adds support for API key authentication in the Operator. The implementation should be similar to what we have is PXC Operator.