Step 898 pod update

[godrei]

Checklist

• [x] I've read and accepted the Contribution Guidelines
• Requires MINOR version update

Context

This PR adds an option for running pod update command, instead of the default pod install.

Resolves: https://github.com/bitrise-steplib/steps-cocoapods-install/issues/49

Changes

• reorganise bitrise.yml wfs (local test wf, ci wf, e2e test case wfs)
• modify test_with_gemfile to test the update command: test_update_with_gemfile
• introduce CocoapodsInstaller and test the pod install phase
• introduce and wire in command input

Investigation details