Add a `LightSyncState` field to the chain spec (#6894)

* Reset code, almost ready for PR

* Improved build_hardcoded_spec

* Fix line widths

* Fix tests

* Fix sc-service-test

* Suggestions from code review

* Rename to LightSyncState

* It's not syncing :^(

* It syncs!

* Remove rpc call

* Convert spaces to tabs

* Moved sc-service things to export_sync_state.rs

* Fix tests

* Wait for syncing with network_status_sinks

* Remove sc-network from node-template

* Apply suggestions from code review

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>

* Various changes, split the flag up into 2 pieces to make testing easier.

* Update client/cli/src/commands/build_spec_cmd.rs

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>

* Revert a lot of changes

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>