Proto: allow bakers to set a consensus key (part 3/4 : toggle vote)

This MR is the third part of MR !5106 (closed) which implements the consensus key TZIP draft. See the original MR and the corresponding Tezosagora post for more general discussion about the proposed feature.

It adds a toggle vote to deactivate the Drain_delegate operation.

This MR includes !5054 (closed), !5455 (closed), !5456 (closed) and !5168 (closed). Only the following commit needs to be reviewed.

• Proto: add a toggle vote for deactivating Drain_delegate

Chnages in src/proto_alpha/lib_protocol: 12 files changed, 94 insertions(+), 47 deletions(-)

Total changes: 41 files changed, 222 insertions(+), 75 deletions(-)