Update CD Workflow to archive previous releases

[RichDom2185]

Closes #941.

Changes:

• Use github.ref_name instead of unnecessary rlespinasse/github-slug-action
• Auto-generate release tags and titles based on the current time
• Generate changelog from the last release from the same branch
• Archive previous releases using the autogenerated tag name

[coveralls]

coverage: 95.295%. remained the same
when pulling abe896a on RichDom2185:archive-previous-releases
into 18a71d3 on source-academy:master.

[RichDom2185]

@YaleChen299 the issue now is:

• The releases are tagged with the time the workflow was run, not latest-[branch_name]
• While the latest-[branch_name] tag exists and points to the same commit, it does not point to the release,
• So the uploaded asset can't be found when querying from latest-[branch_name]