The `anchors/even` channel type was missing from the grpc bindings.
It is now the default channel type, so `fundchannel` over grpc fails
with:
```
Failed to deserialize response : unknown variant `anchors/even`,
expected one of `static_remotekey/even`, `anchor_outputs/even`,
`anchors_zero_fee_htlc_tx/even`, `scid_alias/even`, `zeroconf/even`
```
Changelog-Changed: Channel type `anchors/even` was added
to the grpc bindings.
It fails because this is an array of enum values, which is a
combination we hadn't seen before. Replacing this with a manually
managed enum, since it is likely we'll want to reuse it in the future.
This is likely inherited from bitcoind, and a bit awkward for us, so
we parse it into a classic struct, but serialize it back into the
bitcoind format when talking to the RPC.
