feat(relay): make filter tag limit configurable

[Thunder-Blaze]

Description

Currently, the maximum number of tag filters per Nostr filter object is hardcoded. This PR introduces a maxTagsPerFilter config option so relay operators can actually bump this limit if they need to.

Issue

• Fixes hardcoded tag limit in filters #150

Testing

1st Response -> When maxTagsPerFilter config was set to 3
2nd Response -> When maxTagsPerFilter config was changed to 4 from 3

• APPS="dbutils relay mesh" make -j4 succeeds locally.

Notes

• The default stays at 3, so there's no behavior change for existing setups unless they explicitly raise the limit (which comes with a matching cost warning in the docs).
• Higher values increase worst-case work when matching tags (see comment in config).

[hoytech]

LGTM, thanks!