feat: Add kms key options to secrets manager instance commands

[s-inter]

Description

relates to STACKITCLI-338

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)

[rubenhoenle]

please fix the pipeline :)

[rubenhoenle]

What about the additional output of the describe command?

[rubenhoenle]

please also adjust the tests of the create command 😅

[github-actions]

Merging this branch will increase overall coverage

Impacted Packages	Coverage Δ	🤖
github.com/stackitcloud/stackit-cli/internal/cmd/secrets-manager/instance/create	57.38% (+6.43%)	👍
github.com/stackitcloud/stackit-cli/internal/cmd/secrets-manager/instance/describe	66.67% (+3.51%)	👍
github.com/stackitcloud/stackit-cli/internal/cmd/secrets-manager/instance/update	57.14% (+8.36%)	👍

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Coverage by file

Changed files (no unit tests)

Changed File	Coverage Δ	Total	Covered	Missed	🤖
github.com/stackitcloud/stackit-cli/internal/cmd/secrets-manager/instance/create/create.go	57.38% (+6.43%)	61 (+8)	35 (+8)	26	👍
github.com/stackitcloud/stackit-cli/internal/cmd/secrets-manager/instance/describe/describe.go	66.67% (+3.51%)	69 (+12)	46 (+10)	23 (+2)	👍
github.com/stackitcloud/stackit-cli/internal/cmd/secrets-manager/instance/update/update.go	57.14% (+8.36%)	56 (+15)	32 (+12)	24 (+3)	👍

Please note that the "Total", "Covered", and "Missed" counts above refer to code statements instead of lines of code. The value in brackets refers to the test coverage of that file in the old version of the code.

Changed unit test files

• github.com/stackitcloud/stackit-cli/internal/cmd/secrets-manager/instance/create/create_test.go
• github.com/stackitcloud/stackit-cli/internal/cmd/secrets-manager/instance/describe/describe_test.go
• github.com/stackitcloud/stackit-cli/internal/cmd/secrets-manager/instance/update/update_test.go