Orderer v3: remove solo support

[tock-ibm]

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

[SamYuan1990]

will we remove solo support in fabric v3 ? hence for local development env, will use raft with a single node?

[rasc0]

Documentation needs to be updated to reflect deprecation of solo consensus protocol. See this page for an example of a tutorial page still referencing solo orderer