## Issue Addressed
Closes#3404 (mostly)
## Proposed Changes
- Remove all uses of Warp's `and_then` (which backtracks) in favour of `then` (which doesn't).
- Bump the priority of the `POST` method for `v2/blocks` to `P0`. Publishing a block needs to happen quickly.
- Run the new SSZ POST endpoints on the beacon processor. I think this was missed in between merging #4462 and #4504/#4479.
- Fix a minor issue in the validator registrations endpoint whereby an error from spawning the task on the beacon processor would be dropped.
## Additional Info
I've tested this manually and can confirm that we no longer get the dreaded `Unsupported endpoint version` errors for queries like:
```
$ curl -X POST -H "Content-Type: application/json" --data @block.json "http://localhost:5052/eth/v2/beacon/blocks" | jq
{
"code": 400,
"message": "BAD_REQUEST: WeakSubjectivityConflict",
"stacktraces": []
}
```
```
$ curl -X POST -H "Content-Type: application/octet-stream" --data @block.json "http://localhost:5052/eth/v2/beacon/blocks" | jq
{
"code": 400,
"message": "BAD_REQUEST: invalid SSZ: OffsetOutOfBounds(572530811)",
"stacktraces": []
}
```
```
$ curl "http://localhost:5052/eth/v2/validator/blocks/7067595"
{"code":400,"message":"BAD_REQUEST: invalid query: Invalid query string","stacktraces":[]}
```
However, I can still trigger it by leaving off the `Content-Type`. We can re-test this aspect with #4575.
249f85f1d9