chore(ci_visibility): add telemetry to the new plugin, part 1

[vitor-de-araujo]

Description

This PR:

• Changes HTTP methods to detect and report errors in a cleaner way. Previously we returned a tuple with the response object and response data, but depending on the error (e.g., connection refused), we might not even get a response object, and we would pass on the exception raised by the http.client module instead. Now the BackendConnector request methods return a BackendResult, containing information about the response and any errors that may have happened, even if there is no response.
• Adds retry logic, based on the reported error types.
• Adds telemetry for HTTP requests, using the reported error types, request duration and other data. Telemetry uses the telemetry_writer from ddtrace.internal.telemetry.

Telemetry for things besides HTTP requests will be added separately.

Testing

Unit tests.

Risks

None.

Additional Notes

None.