Create provider fo output-type frequency

[fpetersen-gl]

Keep track of the output-types' frequency, in case telemetry is enabled. So we count how many outputs of each type are used by the system and report that.

Description

This PR simply calls an already existing method in the OutputService (which I made a bit more readable), converts it into a TelemetryEvent and returns that to the TelemetrySubmissionPeriodical.
Fixes Graylog2/graylog-plugin-enterprise#12203

Motivation and Context

How Has This Been Tested?

There's a test and the code also ran on a local instance, the metric does end up in posthog.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Refactoring (non-breaking change)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have requested a documentation update.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.