Add ability to stage all contracts

[jribbink]

Problem

Developers have expressed a desire to stage all of their contracts using one command, in order, instead of staging individually. This helps prevent validation errors, tedious ordering, running multiple commands, and potentially forgetting to stage contracts

Acceptance Criteria

Some command exists to stage all contracts. (maybe this is default behaviour for flow migrate stage-contract, although, it sounds a bit odd in the singular. Maybe flow migrate stage-contract --all, etc.)

Context

Mentioned and strongly supported during developers office hours.