[Feature]: Artifact Rename + Helm Repo

[ikreymer]

What change would you like to see?

To help smooth changeover from 'browsertrix-cloud' to 'browsertrix', there should be a Helm Repo which allows for updating to the latest release, based on releases in GH.
Part of #1241

The Repository consists of an index.yaml generated somewhere on the static site, eg. docs.browsertrix.com/helm-repo/index.yaml

Context

The published helm chart release artifacts are named browsertrix-cloud-$VERSION. We want to switch them to browsertrix-$VERSION for consistency with the new name.

Creating a helm repository index will allow for smooth transition to new name, and also make it easier to upgrade to new versions.