chore(deps): update redis docker tag to v8

[renovate]

This PR contains the following updates:

Package	Update	Change
redis (source)	major	7.4-alpine → 8.10-alpine

⚠️ This bumps the upstream image (tag + digest) only. Before merging, also bump the Hola bundle version (src/<app>/package.json + src/<app>/src/manifest.json — Hola's semver describes impact on the Hola user, not upstream's number) and review whether the manifest's upgrade/backup blocks need changes. CI regenerates catalog.json on merge.

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[pofallon]

Held for a decision rather than merged with the rest of the batch — flagging what turned up while working through the other Renovate PRs.

redis:7.4-alpine here is the broker for paperless-ngx (Celery) and postiz (BullMQ), both with a persistent ${HOLA_APP_DATA}/redis:/data volume.

Neither upstream project ships Redis 8:

App	What upstream pins today
paperless-ngx	docker.io/valkey/valkey:9-alpine — they moved off Redis entirely
postiz	redis:7.2

So taking this PR puts both bundles ahead of what either upstream tests against, for a component used purely as a queue/cache. Redis 8 is protocol-compatible and both Celery and BullMQ would almost certainly work — but the RDB format bump makes it one-way for that data volume, and there is no functional gain here to justify being first.

The 7.4 line is also still actively maintained: #122 (a fresh 7.4-alpine digest rebuild) landed today.

Recommendation: hold this. The more interesting follow-up is that paperless-ngx upstream has switched its broker to valkey:9-alpine — matching that is a better-motivated change than jumping to Redis 8, and it is the direction upstream actually validates.

Leaving this open rather than closing it, so Renovate keeps it visible for whenever the picture changes.