Upgrading openapi-generator

[Fryguy]

@zitnik @alescernivec I'd like to upgrade the openapi-generator in this repo, mostly so I can pull in the changes made in OpenAPITools/openapi-generator#22052, which reduces the gem size significantly (a quick local test shows the lib dir size drop from 91MB to 51MB!!), as well as the built-in autoload functionality and other bug fixes

However, I'd also like to get this repo into a pattern where we automatically keep it up updated as well, and just wanted you to be aware of the set of PRs I plan to make. In addition, Travis is dead, so I'd like to upgrade to GitHub Actions. Here the full set of changes I'm planning. I'd love your thoughts on this.

• Switch to GitHub Actions #21 Upgrade the repo to GitHub Actions from Travis
• Upgrade openapi-generator to 7.17.0
• Dynamically pull in the latest openapi spec from https://intersight.com/apidocs/downloads/#
• Add a GitHub Action to automatically update the gem weekly similar to https://github.com/ManageIQ/kubevirt-sdk-ruby/blob/989f89aaeb3a9eedacc3b28cde815880f9a123c5/.github/workflows/openapi-generate.yml
• Allow the automated process to update to the latest openapi spec.

cc @agrare @gberginc

[alescernivec]

@Fryguy Sorry for not getting back earlier. I think this is a nice update, unfortunately I can not help with review/merge process on the repo since I don't have the permissions anymore. @gberginc should be able to help here.