rapu: fire shutdown metric on app shutdown

[nosahama]

About this change - What it does

• we add the karapace_shutdown_count metric, to the base app and fire the metric on app shutdown
• the close_by_app() is added to the app shutdown hooks and thus is called on app shutdown

Shutdown logs

Active shutdown alert after 2 manual shutdowns

Firing shutdown alert after 2 manual shutdowns

Why this way

This way we have a metric to count the app shutdown ands this is handled on the app server level, rather than in application code.

[eliax1996]

LGTM, nice great job!

[nosahama]

LGTM, nice great job!

Thanks man, I was thinking in another iteration, we can add labels to the shutdown metric, i.e. the reason for the shutdown, maybe set the error on the app object and reference the error when we fire the shutdown metric or leave it empty which will denote a normal expected shutdown, we can improve 👍

[github-actions]

Coverage report

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File	Statements	Missing	Coverage	Coverage (new stmts)	Lines missing
karapace
config.py
rapu.py
statsd.py
Project Total

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