fix: alertmanager: validate labels and annotation names only, not values

[hileef]

What type of PR is this?

/kind bug

Any specific area of the project related to this PR?

/area config

What this PR does / why we need it:

Only validate Prometheus Label names and Annotation names instead of validating values as well.
Internally, Alertmanager and Prometheus use the same data model to represent both labels and annotations,
and apply the same validation logic.

See official doc here : https://prometheus.io/docs/concepts/data_model/#metric-names-and-labels, which mentions :

Label names may contain ASCII letters, numbers, as well as underscores. They must match the regex [a-zA-Z_][a-zA-Z0-9_]*. Label names beginning with __ are reserved for internal use.

Label values may contain any Unicode characters.

As a practical example, we encountered an issue because we use dashes in our label values,
such that this was rejected : extralabels: "cloud:aws,region:eu-west-1,team:platform"

Special notes for your reviewer:

Hello, we are currently in the process of experimenting with this project for internal usage ;
it looks quite promising, great work 💪 😄

We encountered an issue when trying to use our standardized internal alert routing,
which should be fixed with these changes 🙏

It wasn't obvious to me where to add a test for such a bug fix,
I may have missed something but could not find config validation tests
so I didn't add one for this specific use case, I hope that's okay.

[poiana]

Welcome @hileef! It looks like this is your first PR to falcosecurity/falcosidekick 🎉

[Issif]

Thanks and sorry for the delay I was sick for past few days

[poiana]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: hileef, Issif

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• OWNERS [Issif]

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[poiana]

LGTM label has been added.

Git tree hash: cbfb5439a48a68be7a18f5838a2fd6fb1782fbd2

[hileef]

Thanks and sorry for the delay I was sick for past few days

No problem 🙏 Glad to hear you are doing better @Issif 🙂

I'm not sure how to proceed with this PR though, I do notice that there are "3 workflows awaiting approval" 🤔
Is this PR experiencing something similar to #431 (comment) ?

Is there something I can do to help ? 🙂

[Issif]

Thanks.

The merge should be automatic after my approval, let me check