prometheus metrics for server mode

[sbrunato]

trafficstars

Implement prometheus metrics for server mode

Should be configurable as needed only in containers.

measure data downloaded from each provider measure product types searched ?

check https://github.com/trallnag/prometheus-fastapi-instrumentator

[alambare]

additional suggested measures:

• count of available providers
• count of available product types

[alambare]

Metrics should be OpenTelemetry as it's more general and the new standard way of doing things.

[dalpasso]

Metrics are implemented with OpenTelemetriy automatic instrumentation (https://opentelemetry.io/docs/instrumentation/python/automatic/).

TODO:

• Compare with https://github.com/open-telemetry/opentelemetry-python-contrib/blob/main/CONTRIBUTING.md#guideline-for-instrumentations
• Handle exceptions raised in the metric's code. Write a log message with the error.
• Add test.
• Cleanup of the code. For example, _instrument_search and _instrument_download used to be independent of each other (you could call _instrument_search without calling _instrument_download) but this is not the case anymore. This is not clear for the code and it should be rewritten.
• Fix EODAGInstrumentor_uninstrument. The callback functions continue to be called after calling _uninstrument