exp run: rename --run-all to --all

[shcheklein]

Command:

dvc exp run --run-all

looks weird, what was the reason to not name it

dvc exp run --all

or even:

dvc exp run --queue to be consistent with remove and gc?

[pmrowla]

Essentially both exp run --run-all and exp run --queue haven't been touched since the entire exp feature was experimental (before any release), and they both predate the current iterations of exp remove and exp gc.

I think the --queue/--run-all (and --temp) flags should eventually just go away entirely in favor of a proper solution for #5615

[dberenbaum]

dvc exp run --all is already a valid command apparently, although I don't know what this flag is intended to do and am having trouble figuring out where it comes from.