Orderer v3: remove solo support

In v3 we will remove support for the solo consensus protocol.

- [x] Disable solo as a consensus protocol
- [x] Change integration tests that use solo to single node raft
- [x] Change integration tests that do consensus type migration to check limited functionality (maintenance mode)
- [x] Remove integration tests that use solo but do not add value
- [x] Remove solo from integration tests infrastructure
- [x] orderer server main unit test uses a solo-based process
- [x] Remove solo code from orderer / consensus
- [x] Clean up the code for kafka to raft migration, but keep some features of it that may be useful for migration from protocol to protocol (e.g. raft -> bft)
- [ ] Some unit tests use a solo config tx (genesis usually), change them to use single node raft
- [ ] Remove solo from local config objects and methods
- [ ] Remove solo from (shared) channel config objects and methods
- [ ] Remove solo kafka from configtxgen
- [ ] #4496
- [ ] Remove/deprecate solo from documentation

In Epic #3511