e7bf705f68
These are secret menu items. To use them:
* Metric of type: labeled_counter
* `telemetry_mirror` must have `h#` prefix before the histogram
* For categorical:
* Samples must always be 1, or we'll assert
* Labels must be specified in both probes with the same spelling, case, and
order
Tests have been added to t/c/t/tests/python/test_mirrors.py to ensure these
restrictions are adhered to.
Differential Revision: https://phabricator.services.mozilla.com/D232662