Add region-specific warnings for one-time read application keys in AP2 and GovCloud

[anthony-dgx]

API and Application Keys documentation (content/en/account_management/api-app-keys.md):

• Added conditional formatting using {{< site-region region="ap2,gov" >}} to show one-time read warning only for AP2 and GovCloud users
• Removed redundant note from the Notes section
• Service Accounts documentation (content/en/account_management/org_settings/service_accounts.md):
• Updated existing warning to use conditional formatting with {{< site-region region="ap2,gov" >}}
• Warning now only appears for users who have selected AP2 or GovCloud regions

What does this PR do? What is the motivation?

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• Ready for merge

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Additional notes

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✅ Documentation Team Review

The documentation team has approved this pull request. Thank you for your contribution!

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Modified Files

• https://docs-staging.datadoghq.com/anthony.dagneaux/otr-govcloud-ap2/account_management/api-app-keys
• https://docs-staging.datadoghq.com/anthony.dagneaux/otr-govcloud-ap2/account_management/org_settings/service_accounts