Add schema to APM data telemetry

[smith]

In #70180 APM is listed as one of the telemetry collectors where we have a missing schema. The schema was added in #71112 but there are some issues:

• APM is excluded in the X-Pack telemetry configuration
• Since we're calling the function to get the schema and it's not inline in the file, the parser fails to parse the schema because the telemetry_check script is parsing the files

Make the telemetry_check script run and pass on APM and properly notify the Telemetry team in pull requests when changes are made to the schema.