Onboarding Intake(2/3): Onboard intakes resource

[devanshcache]

Description

This PR onboards the new STACKIT Intake (ticket) service into the Terraform provider.

Intake is composed of three components:

Intake Runners: dedicated, isolated runtime data ingestion environment
Intakes: a specific data stream or topic within an Intake Runner
Intake Users: provides secure access credentials for your applications to connect to your Intake

This PR contains the Intakes part only to make a quicker and less overwhelming review.

Checklist

• Issue was linked above
• Code format was applied: make fmt
• Examples were added / adjusted (see examples/ directory)
• Docs are up-to-date: make generate-docs (will be checked by CI)
• Unit tests got implemented or updated
• Acceptance tests got implemented or updated (see e.g. here)
• Unit tests are passing: make test (will be checked by CI)
• No linter issues: make lint (will be checked by CI)

[cgoetz-inovex]

Hi @devanshcache ,
thanks for your contribution, I've created an internal tracking issue for the review of your changes

[devanshcache]

Hi @cgoetz-inovex, Thank you looking forward for your feedback :)