Add GenieACS / MongoDB sample

[GeiserX]

Summary

Adds a basic Compose sample for GenieACS, an open-source TR-069 (CWMP) Auto Configuration Server used to remotely manage CPE devices (routers, ONTs, gateways). This fills a gap in the collection — there is currently no network device management / TR-069 sample.

Proposed and discussed in #691.

Scope

Per the feedback on #691, this is kept as a minimal local/dev sample (listed under "Basic setups… not production ready"):

• genieacs-mongodb/compose.yaml — genieacs + mongo only

• genieacs-mongodb/README.md

• one entry in the root README.md

• MongoDB is internal (expose, not published on the host); only the GenieACS ports (7547/7557/7567/3000) are mapped.

• The README flags that the sample is not production ready, and that the GENIEACS_UI_JWT_SECRET and database credentials must be replaced before real use.

Test plan

• docker compose config validates
• docker compose up -d — MongoDB becomes healthy, GenieACS starts
• GenieACS UI returns HTTP 200 on http://localhost:3000
• MongoDB confirmed not reachable on the host (internal 27017/tcp only)
• docker compose down -v cleans up

Closes #691

[vaguul]

I looked through the PR diff and this matches the scope discussed in #691.

The parts that matter for maintainer review are in place:

• sample is listed under the basic/not-production-ready section
• MongoDB is internal via expose, not published on the host
• the README calls out replacing GENIEACS_UI_JWT_SECRET and enabling Mongo auth before real use
• the PR body includes the validation checklist, including UI 200 and Mongo not exposed on the host

No extra scope concerns from me. This is much easier to review than a production-oriented sample would have been.