try-runtime-cli: nudge users to use snapshots

[liamaharon]

Related #13975

The 'straight forward' way of getting commands like execute-block, on-runtime-upgrade, etc to work is using live ws://host-uri. However, it can be quite slow.

If a developer wants to run these commands repeatedly, it's much more efficient to run create-snapshot once to create a snapshot, and thereafter use the snapshot instead of fetching the live state each time. Snapshots load most of the time <1s.

Developers are sometimes not aware of the benefit of snapshots, I suggest nudge them with some logs when they use live. Something very roughly along the lines of:

INFO: If you are repeatedly running this command with the live option, you may benefit from using snapshots which have close to instantaneous load times.
INFO: 1. Create a snapshot with try-runtime-cli create-snapshot <good arg suggestions>
INFO: 2. Next time you run this command, replace live ws://<their-node-uri> with snap node-state.snapshot

---

          I was thinking when someone executes a command like `on-runtime-upgrade live ws://...`, they probably want to take a snapshot and from then on use `snap` instead of `live`. Not sure why the sync mode would matter, maybe I misunderstand?

_Originally posted by @liamaharon in paritytech/polkadot-sdk#174

[liamaharon]

Moved to paritytech/try-runtime-cli#13