Add more supported l5d paths for libpvarki

[niilovuo]

User-Facing Summary

• Added possibility of fail-closed l5d if header not present, can be controlled via env
• Added proper path for ingress (traefik), we need to validate the X header for the callsign even if l5d header is present.
• Added tests for L5D header paths and simplified tests with pytest parametrization

Why It's Good for the Product (Release Goal)

• Improves linkerd integration, allows us to mesh ingress pods as well (which allows us to create stricter access controls)

Anything Else You'd Like to Mention

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