This commit refactors 2 new custom commands to work more like the native env command, allowing for multiple environment variables to be set.
Additionally, the documentation on acceptance tests have been expanded to list out custom commands.
These are initial testscripts for confidence around core `gh secret` subcommands around 1) repository, 2) repository environment, 3) organization secrets.
Each testscript exercises the 3 core subcommands of `gh secret`: 1) setting, 2) listing, and 3) deleting each type of secret.
Note should be made that repository environments do not exist for free accounts such as `gh-acceptance-testing`.
