Adding back priority label for Alertmanager outputs

[tks98]

What type of PR is this?

Uncomment one (or more) /kind <> lines:

/kind bug

/kind cleanup

/kind design

/kind documentation

/kind failing-test

/kind feature

Any specific area of the project related to this PR?

Uncomment one (or more) /area <> lines:

/area build

/area config

/area outputs

/area tests

What this PR does / why we need it:

This PR adds back the priority label for alertmanager outputs. Release 2.25.0 was supposed to resolve #276 and add it but priority was replaced with eventsource.

Fixes #339

Special notes for your reviewer:

[poiana]

Welcome @tks98! It looks like this is your first PR to falcosecurity/falcosidekick 🎉

[Issif]

I let you sign off your commit and I'll approve.

git commit -s --amend && git push origin master -f

[tks98]

I let you sign off your commit and I'll approve.

git commit -s --amend && git push origin master -f

Had to sign off my first commit also since there were two. Please let me know if anything else is required. Thanks!

[poiana]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Issif, tks98

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[poiana]

LGTM label has been added.

Git tree hash: 5a241a3fe09ce935bab8bb19ff95412464ed52e5