feat(auth-server): tag auth.strategy.used metric with route path

[vbudhram]

Because

• The Hawk to Bearer token migration could not be observed per endpoint; the auth.strategy.used counter carried only scheme and kind, so adoption couldn't be broken down by route.

This pull request

• Adds a templated path tag to auth.strategy.used in the Hawk and Bearer FxA-token schemes (hawk-fxa-token.js, bearer-fxa-token.js).
• Uses req.route.path (templated route, never the raw URL) so cardinality stays bounded at ~2 schemes × authed routes.
• Falls back to path:unknown when the route is unavailable.
• Updates hawk-fxa-token.spec.ts and bearer-fxa-token.spec.ts to assert the new tag.

Issue that this pull request solves

Closes: https://mozilla-hub.atlassian.net/browse/FXA-13948

Checklist

• My commit is GPG signed.
• If applicable, I have modified or added tests which pass locally.
• I have added necessary documentation (if appropriate).
• I have verified that my changes render correctly in RTL (if appropriate).
• I have manually reviewed all AI generated code.

Other information

• Metric change only; no behavior change to authentication. Per-endpoint adoption becomes visible in StatsD/Grafana once deploy

[Copilot]

Pull request overview

This PR improves observability of the ongoing Hawk → Bearer FxA-token migration by adding a bounded-cardinality path tag (templated route path) to the auth.strategy.used StatsD counter, enabling per-endpoint adoption tracking.

Changes:

• Tag auth.strategy.used with path:${req.route?.path ?? 'unknown'} in both Hawk and Bearer FxA-token auth schemes.
• Update Hawk and Bearer auth-scheme unit tests to assert the new path tag is included in the emitted metric.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
packages/fxa-auth-server/lib/routes/auth-schemes/hawk-fxa-token.js	Adds path tag to the auth.strategy.used increment for Hawk auth.
packages/fxa-auth-server/lib/routes/auth-schemes/bearer-fxa-token.js	Adds path tag to the auth.strategy.used increment for Bearer auth.
packages/fxa-auth-server/lib/routes/auth-schemes/hawk-fxa-token.spec.ts	Extends metric assertion to include the new path tag.
packages/fxa-auth-server/lib/routes/auth-schemes/bearer-fxa-token.spec.ts	Extends metric assertion to include the new path tag.

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