Add Lumra webhook template

[bradpulseir]

Summary

Adds a webhook template for Lumra (https://privinet.net), a service by PriviNet that seals incoming events into tamper-evident, independently verifiable records. Pointing the uplink message at Lumra gives users a signed, hash-chained record of each uplink, with an exportable proof bundle that can be verified offline.

Changes

• Add lumra.yml webhook template (uplink messages only)
• Register lumra in templates.yml

Notes for Reviewers

The endpoint accepts The Things Stack v3 uplink JSON as-is at https://api.privinet.net/v1/ingest/raw. Authentication is a bearer API key from self-serve signup, exposed as a secret api_key template field and injected into the Authorization header.

Tested today against a live The Things Stack Sandbox (nam1) application: a custom webhook configured with exactly the base URL, path, and header from this template delivered simulated uplinks; each returned HTTP 200 and produced a sealed, signature-verified record on the Lumra side. Integration docs for users are at https://privinet.net/api.html.

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[PriviNet1]

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[PriviNet1]

Superseded by #115.