fix(json-specs): add secret flags on all secret fields

[Yqnn]

What does this PR do?

Add secret flag on all the sensitive fields so that they can be treated as secrets by Fleet Automation.

Motivation

https://datadoghq.atlassian.net/browse/FA-1028

Review checklist (to be filled by reviewers)

• Feature or bugfix MUST have appropriate tests (unit, integration, e2e)
• Add the qa/skip-qa label if the PR doesn't need to be tested during QA.
• If you need to backport this PR to another branch, you can add the backport/<branch-name> label to the PR and it will automatically open a backport PR once this one is merged

[github-actions]

⚠️ Recommendation: Add qa/skip-qa label

This PR does not modify any files shipped with the agent.

To help streamline the release process, please consider adding the qa/skip-qa label if these changes do not require QA testing.

[chatgpt-codex-connector]

Codex usage limits have been reached for code reviews. Please check with the admins of this repo to increase the limits by adding credits.
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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.85%. Comparing base (f2c29c5) to head (d936e7f).
⚠️ Report is 21 commits behind head on master.

Additional details and impacted files

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[steveny91]

Looks good. Can you add a changelog for datadog_checks_dev?

Review from steveny91 is dismissed. Related teams and files:

• agent-integrations
  • datadog_checks_dev/changelog.d/21975.fixed