[Uptime] Add mapping for REST API test data

[justinkambic]

Summary

Mappings are currently absent for the data directory we use for Uptime's REST API. This caused some problems when backporting other test-related changes to 7.x. Specifically, certain values were being counted that would have been ignored if the proper mappings were present, which broke some API tests.

Rather than modifying that backport PR post-review to make it work, I decided it was better to open a PR to add the necessary mapping file to master first, and then backport it with an updated version number to 7.x. At that point I can remove the added mapping from the above-linked PR and retest only those changes.

Testing

If this is passing CI then it should be ok to merge.

Checklist

Use strikethroughs to remove checklist items you don't feel are applicable to this PR.

• This was checked for cross-browser compatibility, including a check against IE11
• Any text added follows EUI's writing guidelines, uses sentence case text and includes i18n support
• Documentation was added for features that require explanation or tutorials
• Unit or functional tests were updated or added to match the most common scenarios
• This was checked for keyboard-only and screenreader accessibility

For maintainers

• This was checked for breaking API changes and was labeled appropriately
• This includes a feature addition or change that requires a release note and was labeled appropriately

[elasticmachine]

Pinging @elastic/uptime

[elasticmachine]

💚 Build Succeeded

• continuous-integration/kibana-ci/pull-request

[spalger]

LGTM

[justinkambic]

Backported to:
7.1.0/7.x e0a488c
#35290