Add offline support

[lpusok]

Checklist

• [x] I've read and followed the Contribution Guidelines
• [ ] README.md is updated with the changes (if needed)

Version

Requires a MINOR version update

Context

Added steps command with subcommands:

  list-cached     List all the cached steps
  preload         Makes sure that Bitrise CLI can be used in offline mode by preloading Bitrise maintaned Steps.

The preload can be configured like this:

NAME:
   bitrise steps preload - Makes sure that Bitrise CLI can be used in offline mode by preloading Bitrise maintaned Steps.

USAGE:
   Use the BITRISE_OFFLINE_MODE env var to test after preloading steps.

OPTIONS:
   --steplib-url value    URL of the steplib to list or preload steps from (default: "https://github.com/bitrise-io/bitrise-steplib.git")
   --maintainer value     Maintainer of the steps to list or preload (default: "bitrise")
   --majors value         Include X latest major versions (default: 2)
   --minors value         Include X latest minor versions for each major version (default: 1)
   --minors-since value   Include latest patch version of minors that were released in the last X months (default: 2)
   --patches-since value  Include all patch version that were released in the last X months (default: 1)

Changes

Investigation details

Decisions