Allow specification of experiment runner version using release tag instead of commit SHA

Nobody has claimed this yet.

# TL;DR
Allow researchers to specify an experiment runner version using a release tag instead of a commit SHA

# Narrative
As a researcher, I would like to keep my experiment runner up to date and understand if there are new features or bugfixes that I would benefit from, but it's hard to tell what I'm using compared with the latest release. This makes it harder to know e.g. which release notes to look through.

As a maintainer of the ember-lookit-frameplayer codebase, I would like to be able to see more clearly which versions are in active use.

# Acceptance Criteria

- [ ] Researcher can specify release tag for experiment runner version
- [ ] Release tag is stored and visible as metadata, either replacing or in addition to commit SHA
- [ ] Data is fetched and displayed about commit corresponding to release tag, as with commit SHA currently
- [ ] Researcher can still specify commit SHA instead if desired

Start by locating the existing experiment runner commit-SHA handling and the code that stores and displays its metadata. Trace how commit data is fetched, then determine where release tags can be accepted while preserving SHA input. Done means tags and SHAs both work, the tag and corresponding commit metadata are visible, and the acceptance criteria are covered by tests.

Written by the indexing model from the issue text.