Add PuppetCore gem source support to gem_ci and tools_mend_ruby workflows

[gavindidrichsen]

Overview

This PR is about puppetcore enablement:

• It simplifies the existing puppetcore-enabled module_ci.yml, removing an unnecessary input parameter.
• It enhances gem_ci.yml and tooling_mend_ruby.yml enabling puppetcore.

All updates have been manually tested against puppetcore and non-puppetcore consumers to ensure backward compatibility. For example, this puppet_upgrade PR enables puppetcore and re-uses both the gem_ci.yml and tooling_mend_ruby.yml. Therefore I found 2 non-puppetcore consumers (puppet-strings and puppet_litmus) of these same shared workflows and verified that these consumers also continue to work as expected. The tests results are all below in the PR comments.

Changes

• Removed puppetcore_api_type input parameter because the extra flexibility was not worth the cost of added complexity, I believe.
• Added environment configuration for PuppetCore authentication using PUPPET_FORGE_TOKEN. This "secret" is then in turn used to set the BUNDLE_RUBYGEMS___PUPPETCORE__PUPPET__COM which enables authenticated access to the puppetcore gems

ALSO updated the how to document for consumers of these re-usable modules, see docs/how-to/how_to_inject_puppetcore_authentication_into_the_shared_workflows.md

Impact

• Modules using these workflows can now access private Puppet gems when authorized
• Consuming workflows need to set a valid PUPPET_FORGE_TOKEN secret on their repository
• No breaking changes expected as all new parameters have sensible defaults and the new shared workflows have been verified with both a puppetcore enabled module. See in the comments below for proof of testing.

[gavindidrichsen]

Given that 2 shared workflows have changed in this PR, module_ci.yml and 'gem_ci.yml, I wanted to manually test puppetcore and non-puppetcore against both the module_ci.yml and 'gem_ci.yml

Verification of module_ci.yml

puppetcore repo:

non-puppetcore repo:

Verification of gem_ci.yml

puppetcore repo:

non-puppetcore repo:

[gavindidrichsen]

Given that another shared workflow has changed in this PR, tooling_mend_ruby.yml, I wanted to manually test puppetcore and non-puppetcore against this too

Verification of tooling_mend_ruby.yml

puppetcore repo:

non-puppetcore repo: