[Stack Monitoring] Update APM metric titles

[cachedout]

Summary

Update just the the titles of the graphs. Refs #44001 and #43998

After a discussion in #43998 we decided just to update the titles for 7.4 and to postpone additional work for a later time.

To test this PR, verify that the following graph titles exist on the Overview and Instance pages for APM server monitoring:

Response Count Intake API
Response Errors Intake API
Requests Intake API

Ensure you do not see metrics titled as any of the following:

Response Count
Response Errors
Requests

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/stack-monitoring

[elasticmachine]

💚 Build Succeeded

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

[elasticmachine]

💚 Build Succeeded

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

[chrisronline]

LGTM!

[rayafratkina]

@cachedout @chrisronline @simitt can you please add a release_note label to this PR?

[cachedout]

@rayafratkina Apologies. Label added. :)