fix(release): assign the next prerelease number

[coreybutler]

Summary

• The Community Release form calls the dropdown Release Type and uses General for a normal manifest release.
• Alpha, beta, rc, and hotfix numbers are taken from the next unused GitHub tag. The form no longer asks for a number.
• Hotfix Mainline names the general release the hotfix patches. An empty value uses the latest general release.

Test plan

• Run Release Community Build from this branch with Release Type General and confirm the version is the manifest version.
• Run with Release Type beta and confirm the tag is the next beta, currently v2.0.2-beta.4.
• Run with Release Type hotfix and Hotfix Mainline 2.0.1 and confirm the tag is the next hotfix, currently v2.0.1-hotfix.3.
• Leave Hotfix Mainline empty on a hotfix run and confirm the base is the latest general release.