Update handlers to match stats_prometheus.go

[rubensf]

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/kind bug

/kind cleanup

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What this PR does / why we need it: #1051 updated stats_prometheus.go to replace . for _, but the code that then adds the labels to every instance did not update it, so instances where CUSTOM_FIELDS is set to use a key with .s leads to panics.

Which issue(s) this PR fixes: No Github Issue existing so far.

Fixes #

Special notes for your reviewer:

[poiana]

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

[Issif]

nice catch, thanks for you fix

[poiana]

LGTM label has been added.

Git tree hash: 8a0afd3a68c4cd24adb37f6fbab0b6c9a26d2492

[Issif]

The CI fails:

[poiana]

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[poiana]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: rubensf
Once this PR has been reviewed and has the lgtm label, please ask for approval from issif. For more information see the Kubernetes Code Review Process.

The full list of commands accepted by this bot can be found here.

Needs approval from an approver in each of these files:

• OWNERS

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[poiana]

New changes are detected. LGTM label has been removed.

[poiana]

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