Add support for Docker '--cpus' option

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What does this MR do?

Adds support for --cpus option for Docker executor. Successor of !469 (closed).

Why was this MR needed?

Please read #2101 (closed) for a reference

Are there points in the code the reviewer needs to double check?

Does this MR meet the acceptance criteria?

• Documentation created/updated
• Tests
  • Added for this feature/bug
  • All builds are passing
• Branch has no merge conflicts with master (if you do - rebase it please)

What are the relevant issue numbers?

Closes #2101 (closed)

mentioned in merge request !469 (closed)

@nick.thomas Could you review this?

changed title from Support for Docker '--cpus' option to Add support for Docker '--cpus' option

changed the description

mentioned in merge request !553 (merged)

assigned to @tmaczukin

Looks good overall @tmaczukin, just a couple of comments.

resolved all discussions

@nick.thomas I've updated the MR

assigned to @nick.thomas

assigned to @tmaczukin

Just a couple of tiny things now @tmaczukin

resolved all discussions

@nick.thomas Done!

assigned to @nick.thomas

approved this merge request

merged

mentioned in issue #2491 (closed)