[datadog_api_key] Stop overwriting key values in state when the API omits the key

[tyjet]

When updating or importing API key resources, if the Datadog API does not include the optional computed key field, then the field is overwritten with an empty string in terraform state. The key is immutable so it does not need to be updated once it has been initially set.

Added a check to ensure the field is set before writing it into the response.

Tested manually via integration test against API responses with and without the key field. Updated unit test to match new behavior and not depend on the API returning an optional field.

[jack-edmonds-dd]

/merge

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[jack-edmonds-dd]

/merge

[dd-devflow]

🚂 MergeQueue: pull request added to the queue

The median merge time in master is 1m.

Use /merge -c to cancel this operation!

[dd-devflow]

❌ MergeQueue: This merge request is not mergeable, blocked by github

PR can't be merged according to github policy. It's probably because:

• repository configuration requires approval by code owners, but no code owner approved this PR

If you need support, contact us on Slack #devflow with those details!

[jack-edmonds-dd]

/merge

[dd-devflow]

🚂 MergeQueue: pull request added to the queue

The median merge time in master is 1m.

Use /merge -c to cancel this operation!