Prep for Unified CI

[hisaac]

Checklist

• [x] I've read and followed the Contribution Guidelines
• [x] step.yml and README.md is updated with the changes (if needed)
• [x] Updated terraform config to configure Unified CI
  • See here: https://github.com/bitrise-io/bitrise-github-steps/pull/96
• [ ] Cleanup after merge

Version

Requires a no version update at this time. It will be included in the next release after I add some unit tests.

Context

This migrates this step to our Unified CI, and uplifts the repo to match the checks done for Unified CI.

Changes

• Updates all yaml files to pass yamllint checks
• Adds .yamllint.yml file to configure yamllint
• Adds a couple things to the .gitignore, and sorted it alphabetically
• Refactors bitrise.yml
  • Moves the integration tests to their own file at e2e/bitrise.yml
  • Adds standard check and generate-readme steps
• Updates README.md using the readme generator step
• Changes Go version in go.mod to 1.17 (see inline comment for more details)

[hisaac]

Thank you for the feedback @ofalvai 🙏. I believe I've addressed all of your comments. Let me know if there's anything else.

[hisaac]

Ah, looks like I have to undo some of the changes to the yaml files as well to satisfy our default yamllint config. Will do that ASAP.

• [x] Fix new yamllint errors

[ofalvai]

@hisaac as a newcomer, if you find some of the yamllint rules too strict or meaningless, please raise these issues! We defined our base ruleset once, but we can always iterate on the exact rules to make everyone happy and productive.

[hisaac]

@ofalvai I had to do one more small change to fix the e2e test run, so it dismissed your review.