Grandpa warp sync request-response protocol (#7711)

* Made a start

* So the proof between authority set is phragmen one, this is crazy big,
or is there some signing of the result : that is the storage key, damn?

* ok getting from header digest seems doable.

* for testing

* get set id from storage directly (should use runtime to handler change).

* move test to init

* correct auth key

* fix iteration

* Correct proof content

* actually update block number.

* actually check last justif against its header

* justification relation to new authorities through header hash check is
needed here. This assumes the hash from header is calculated.

* Few changes

* Connected up cheme's branch

* Clean up

* Move things around a bit so that adding the grandpa warp sync request response protocol happens in the node code

* Nits

* Changes to comments

* Cheme changes

* Remove todos and test compile.

* Rename _authority_ related proof function to _warp_sync_ .

* Update client/grandpa-warp-sync/src/lib.rs

quick fix

* Put the warp sync request response protocol behind a feature flag because we dont' need it on a light client.

* Update client/grandpa-warp-sync/src/lib.rs

Quick fix

* Update Cargo.lock

* Adding test, comment on limitation related to 'delay', this could
be implemented but with a cost.

* Set between a delay override last fragment.

* Check for pending authority set change at start.

* adjust index

* custom cache is not a good idea.

* Use a simple cache instead.

* restore broken indentation

* Address crate rename

* Merge conflict badly resolved, sorry

Co-authored-by: cheme <[email protected]>
Co-authored-by: Pierre Krieger <[email protected]>