Fix issues from migrating to clap v3

[nanocryk]

What does it do?

One of the changes of #1319 is the migration from structopt to clap v3 to implement the CLI. However, there are some breaking changes while doing this migration which we were not aware of :

• In 0.9.17 Dependency Upgrade #1319 I had to change Structopt derive to Parser or Subcommand. It failed to compile and I added a clap(flatten) argument. However this made the key subcommand disapear (because it is flatten). Another argument (clap(subcommand)) must be used instead.
• require_delimiter was changed to require_value_delimiter, but also no longer imply require_value_delimiter. It is thus necessary to add it explicitely for our --ethapi argument.
• this breaking change also impact a CLI struct in substrate for try-runtime, which is not fixed upstream. I thus fixed it in our branch, and will make a PR for upstream.
• I finally cherry-picked a commit from upstream that allow again --reserved-nodes to be provided multiple times (instead of using a single one with values separated with ,). I applied this change to both the try-runtime CLI and our --ethapi.

I only updated the substrate branch, since locks of dependencies (polkadot, cumulus, ...) are not accounted for when building moonbeam.

What important points reviewers should know?

Is there something left for follow-up PRs?

What alternative implementations were considered?

Are there relevant PRs or issues in other repositories (Substrate, Polkadot, Frontier, Cumulus)?

What value does it bring to the blockchain users?