fix: display custom schematics in help

[daniel-samson]

PR Checklist

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PR Type

What kind of change does this PR introduce?

[x] Bugfix
[ ] Feature
[x] Code style update (formatting, local variables)
[x] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[ ] Other... Please describe:

What is the current behavior?

Related:
Issue Number: #1433
PR: #1434

Currently, when you run nest generate --help, it will only display schematics from the @nestjs/schematics package. If you have a custom collection configured in nest-cl.json, it doesn't display the schematics from your custom package.

Example:

What is the new behavior?

Example:

After this change, you can see which collection is being selected and a table of schematics from that collection

Does this PR introduce a breaking change?

[ ] Yes
[X] No **

**It changes the commander to load async, and the getSchematics is no longer static, so sort of...

Other information

I have manually tested the local command and the global command, and it seems to work. This change is important to me, as it allows me to easily train my team to use the custom schematics i have made.

I am on the discord (verbing#6551)

[daniel-samson]

@micalevisk Thank you for the comments. They were very helpful. I have made the change you have asked for. Let me know if you need me to make any more changes.

[kamilmysliwiec]

LGTM