Replace terms CSP -> API provider, API invoker -> API Consumer where appropriate

[hdamker]

Problem description

Originally reported by @tanjadegroot in #383 (comment) and further review comments of r1.3.

This is a sub issue of #387

Expected action

Replace the following terms with the ones which are defined within the CAMARA Glossary:

• communication service provider -> API provider (several occurrences across the YAML files)
• API invoker -> API Consumer

Check for further similar needed replacements

Additional context

See also the discussion in #395 (comment) and #395 (comment)