fix custom headers not added to loki output http/s requests

[lsroe]

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?

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/area build

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What this PR does / why we need it:
Adds LOKI_CUSTOMHEADERS to http/s requests as expected

Which issue(s) this PR fixes:

Fixes #1108

Special notes for your reviewer:

[poiana]

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

[Issif]

👍

[poiana]

[APPROVALNOTIFIER] This PR is APPROVED

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

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[poiana]

LGTM label has been added.

Git tree hash: 0c5d553a18bdbac704d842824b019590ba6432df