[PDE-4682] chore(cli): Add @clif/core dependency, upgrade @oclif/plugin-help

[rnegron]

As mentioned in #556 (comment), simply upgrading @oclif/plugin-help will break CLI functionality due to certain helper methods we were using in ZapierBaseCommand being removed. In fact, they were moved over to the @oclif/core library.

This PR adds the @oclif/core dependency, which is also the first step in migrating over from deprecated helper libraries.

A visual difference in how text is formatted can be observed before and after this PR. I'm looking into why this formatting change occurred to see if we can maintain the previous formatting style.

Before (wider terminal):

After (wider terminal):

Before (smaller terminal):

After (smaller terminal):

[rnegron]

Opening for review because I'm not sure it's worth the time to implement changes to make the renderList display as before. The display does look uglier... but I think the tradeoff of closing #555 is worth it.

The reason why the display changes is because the renderList implementation in @oclif/core is different: https://github.com/oclif/core/blob/10b7dc0dd207906df208b0c5b85e309106dd8a5f/src/cli-ux/list.ts#L15, it does not include additional properties like the one from @oclif/plugin-help (which no longer exists after the upgrade).

[eliangcs]

@rnegron I found instead of importing renderList from @oclif/core/lib/cli-ux/list, we should it from @oclif/help/lib/list. That way we can keep using the same renderList with previous options. Turns out @oclif/plugin-help was not gone but was renamed to @oclif/help.

I created #743 to fix. Otherwise, this PR looks good to me. Feel free to find someone else to approve. Thanks!