cmd: update pending target arg descriptions

[jorgeorpinel]

Extracted from #1384 (comment)

Need to double check the following commands to see whether their targets support files/dirs ... repro, run, (un)freeze, remove, unprotect, update, and metrics/plots show

• May imply core repo output string updates as well.

[imhardikj]

@jorgeorpinel I checked the above commands with file/dirs:

• repro: currently being worked on in repro cmdref updates #1861
• For unfreeze, freeze, remove, when I tried them with files/dirs as targets this was the output:
  ERROR: failed to freeze/remove `foobar`- "Stage `foobar` not found inside `dvc.yaml` file"
• update: directories were working when used with dvc update -R else same error as above
• unprotect already excepts files/dirs
• Similarly metrics show also accepts metrics files as targets.
• run: doesn't have targets argument

Does this require updating targets description in the update command or rather just the -R option desc.

[jorgeorpinel]

Similarly metrics show also accepts metrics files as targets.

What about plots show? I'll look into that. UPDATE: See iterative/dvc#4799

Does this require updating targets description in the update command

No, that cmd ref seems to have complete info about -R and dir targets already.

Looks like no major changes are needed...