[FSSDK-9486] maint: Update CI and publishing

[mikechu-optimizely]

Summary

• Large updates to C# CI workflow
• Add release workflow to this repo
• Remove Travis from release build and publish
• Remove AWS S3 for artifact storage and use GitHub's native artifact handling (expires after 90 days, though)

Need to release branch v3.11.3, and I'm taking the opportunity to revamp DevOps

Test plan

• No code paths changed, so unit & integration tests should continue to work
• Review the recent test runs of the workflow

Issues

• FSSDK-9486

[mikechu-optimizely]

This PR needs to be merged BEFORE

357

358

[mikechu-optimizely]

Later, I'll need to remove the CI and deployment secrets supporting AWS uploads.

[mikechu-optimizely]

Temporarily closing to avoid CI runs

[mikechu-optimizely]

LGTM - so I guess with this change, we now can remove the codesign repo completely?

@jaeopt I think we should archive it for sure, so it's not used.

[mikechu-optimizely]

I need to cherry-pick these changes to the PR for the release-3.11.3 branch next.