Update gha to support sto only workflows sto 7577

[douglas-j-bothwell]

Preview link

• Important notes for using GitHub Action and Drone Plugin steps in STO first bullet point
• Also fixes some bad links in Next steps, STO features, Try Harness STO, and STO tutorials (I checked the updated links and confirm that they work)

Prepub checks

PRs must meet these requirements to be merged:

• [ ] Successful preview build.
• [ ] Code owner review.
• [ ] No merge conflicts.
• [ ] Release notes/new features docs: Feature/version released to at least one prod environment.