Restrict frontend-template-site app dependencies to patch-level ranges #562

Description

On the release branch of a Site we cannot assume that a minor version bump of a frontend app still works against that release's backend, and the caret ranges in frontend-template-site allowed exactly that.

The caret ranges on the apps and on frontend-base become x-ranges anchored to the currently locked minor, so the branch accepts patch releases from each maintenance line but declines features. Bug fixes still arrive without intervention, while anything that might require a newer backend now takes a deliberate edit. This is the first application of OEP-10 ADR 0003 to a Site repository.

Part of #560. Proposal: openedx/openedx-proposals#815

Implemented by openedx/frontend-template-site#25