[Bug]: Set the request body payload size limit

[djordon]

Bug - Set the request body payload size limit

1. Description

The signer HTTP server, the one used as an event observer, will reject webhook events where the body exceeds the default limit of 2 megabytes. We need to set the limit to something that is greater than what we could expect from the stacks node.

1.1 Context & Purpose

The stacks-core event observer functionality stalls the node whenever it doesn't get a 200 response from an event observer. With the currently configured sbtc-signer event observer, we will reject events with more than 2 MBs of payload data, returning status code 413, PAYLOAD_TOO_LARGE. This limit should be set to some larger value.

2. Technical Details:

Stacks blocks have a limit of 2 MB, which is enforced at the p2p level (peers reject blocks that are greater than 2 MBs), but event observer events can be larger than that since they contain the subscribed sbtc events. Luckily the size of the sbtc events themselves are bounded by the size of the transactions that create them, so a limit of 8 MB will be fine since it is twice as high as required.

2.1 Acceptance Criteria:

• Raise the payload limit of the sbtc-signer HTTP server.

3. Related Issues and Pull Requests (optional):

The limits in stacks core are P2P codec limits. The one for blocks can be found https://github.com/stacks-network/stacks-core/blob/8ad5e95b85a7b4cbb918e63048f5eea70229e8ce/stackslib/src/net/codec.rs#L482-L498 and https://github.com/stacks-network/stacks-core/blob/c80fa544d176d85a1741b958bc3e11f6c891bf97/stackslib/src/chainstate/stacks/mod.rs#L84-L86