feat: add ResourceManagerApi

[Benjosh95]

Description

The new ResourceManagerApi needs to be manually generated and added for now.

To be able to update the examples and complete this ticket:

• https://jira.schwarz/browse/STACKITSDK-223

Follow-up todo:

Update also examples to use service specific api:

• chore(resourcemanager): update example to use service specific naming #10
• chore(resourcemanager): add examples #14

Checklist

• Issue was linked above
• No generated code was adjusted manually
• Changelogs
  • Changelog in the root directory was adjusted
  • Changelog(s) of the service(s) were adjusted
• VERSION file(s) of the service(s) were adjusted
• Code format was applied: make fmt
• Examples were added / adjusted (see examples/ directory)
• Unit tests got implemented or updated
• Unit tests are passing: make test (will be checked by CI)
• No linter issues: make lint (will be checked by CI)