feat: bound incoming request and add postgres service

[enigbe]

What this PR does

• Adds a PostgreSQL Docker service for the Rust server, removing the need for a local PostgreSQL installation
• Introduces a configurable maximum size limit for incoming request bodies, addressing a previously noted TODO
  • Operators can optionally set maximum_request_body_size in [server_config]
  • Defaults to 10 MB if not specified; capped at 20 MB

[ldk-reviews-bot]

I've assigned @tankyleo as a reviewer!
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Once they submit their review, I'll check if a second reviewer would be helpful.

[tnull]

This seems very conservative, given that monitors could get quite large. Given that the VSS service is actually a storage service, it also might make sense to make this configurable (in contrast to lightningdevkit/ldk-server#80, but even there we set the limit to 10MB).

[tnull]

As mentioned elsewhere: I guess a static upper bound is a good first step, but if we're really concerned about DoS we might need some dynamic rate limiting on a per-IP basis. Although then the question becomes how much of that should be considered the concern of the VSS service itself, and how much we'd just expect users to slap a load balancer/Cloudflare in front of the service to handle that for them

[enigbe]

I've made the configuration changes suggested here, capping at 20 MB for the maximum size.

[ldk-reviews-bot]

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[ldk-reviews-bot]

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