Update outdated GRANDPA pallet docs.

* fix(spellcheck): test of fixing

* fix(hunspell): improved many typos etc.

* fix(hunspell): all errors solved

* fix(hunspell): extended scope of files - the build should fail

* Return error code.

* Fix spelling, sort dictionary.

* fix(hunspell): added fix to gitlabs check

* fix(typo): one typo and test of verification on github

* fix(typo): one typo

Co-authored-by: Tomasz Drwięga <[email protected]>

* message dispatch support multiple instances

* Move pallet-bridge-dispatch types to primitives

* remove pallet-bridge-dispatch dependency

* Update cargo.lock (remove pallet-bridge-dispatch in substrate-relay)

* remove extra dependencies

* Rename `pallet-finality-verifier` to `pallet-bridge-grandpa`

* Missed some CamelCase ones

* Update logging target in GRANDPA pallet

* Rename `pallet-bridge-call-dispatch` to `pallet-bridge-dispatch`

* Rename the dispatch pallet folder

* Update logging target in Dispatch pallet

* Missed a couple

* Format the repo

* Stop listing individual pallets in Compose logs

* Use correct pallet name in module doc comments

* Add `pallet-bridge-dispatch` to README project layout

* Sort crate names in TOML files

* Rename `pallet-bridge-grandpa` runtime Call alias

* use runtime:: prefix for message-lane pallet traces

* renamed message-lane (module and primitives) folder into messages

* replace "message lane" with "messages" where appropriate

* High level docs - start.

* Clean up README

* Start adding details to high level docs

* More docs on the header sync pallet

* Testing scenarios document.

* Add some scenarios.

* Add multi-sig scenario.

* Start writing about message dispatch pallet

* Move content from old README into PoA specific doc

* Apply suggestions from code review

Co-authored-by: Andreas Doerr <[email protected]>

* GRANDPA for consistency.

* Describe scenario steps.

* WiP

* Add notes about block production and forks

* Update.

* Add sequence diagram for Millau to Rialto transfer

* Clean up header sync pallet overview

* Remove leftover example code

* Clean up testing scenarios and amend sequence diagram.

* Linking docs.

* Add some more docs.

* Do a bit of cleanup on the high-level docs

* Clean up the testing scenario

* Fix typos in flow charts

* Fix small typo

* Fix indentation of Rust block

* Another attempt ...