Improve support for the Federation Extension

[m-mohr]

In the EOEPCA+ project, we made an evaluation of the federation-related functionality available through the openEO JS/TS client.
The Federation Extension can be found here: https://github.com/Open-EO/openeo-api/blob/draft/extensions/federation/README.md

The following issues have been identified:

• federation:missing can't be accessed through the corresponding functions for the following endpoints:
  • GET /jobs/:id/logs
  • GET /services/:id/logs
• federation:backends can't be accessed through the corresponding functions for the following endpoints:
  • POST /validation - see also Clarified the behaviour of federation:backends for POST /validation openeo-api#552

[m-mohr]

Implemented.