feat(config): add ignore-existing for profile create

[dergeberl]

Description

This PR adds --ignore-existing as a flag for stackit config profile create in order to call the create idempotent and don not get a error in case the profile already exists. That make it possible to use profiles in automation/tool.

Example: I am currently integrating stackit(-cli) into the gardenctl (gardener/gardenctl-v2#669).

Checklist

• Issue was linked above
• Code format was applied: make fmt
• Examples were added / adjusted (see e.g. here)
• Docs are up-to-date: make generate-docs (will be checked by CI)
• 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)