Make payload/output offloading threshold size and other limits customizable

[ericallam]

Right now everything is hardcoded, but we really need to make these env vars and document them for self-hosters:

https://github.com/triggerdotdev/trigger.dev/blob/04645e83293ab8a04a094a84697b20b2b08d6142/packages/core/src/v3/limits.ts#L3-L11

[askadityapandey]

Can I work on this one? The Project seems pretty cool.