Add telemetry counter for Astarte services APIs calls

[eddbbt]

Add counter for APIs calls via a Plug, gouped by realm name, for the following services: appengine_api, housekeeping_api, pairing_api, realm_management_api

rewrote of routes for realm_management_api (endpoints has been kept the same)

resolve #897

[codecov[bot]]

Codecov Report

Attention: 6 lines in your changes are missing coverage. Please review.

Comparison is base (595adbd) 68.33% compared to head (3c6cd25) 68.34%.

Files	Patch %	Lines
...api/lib/astarte_realm_management_api_web/router.ex	75.00%	2 Missing :warning:
...ngine_api_web/plug/telemetry_calls_counter_plug.ex	75.00%	1 Missing :warning:
...eping_api_web/plug/telemetry_calls_counter_plug.ex	66.66%	1 Missing :warning:
...iring_api_web/plug/telemetry_calls_counter_plug.ex	75.00%	1 Missing :warning:
...ement_api_web/plug/telemetry_calls_counter_plug.ex	75.00%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #900 +/- ## ========================================== + Coverage 68.33% 68.34% +0.01% ========================================== Files 270 274 +4 Lines 7046 7061 +15 ========================================== + Hits 4815 4826 +11 - Misses 2231 2235 +4 ```

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