Notify a user that a new serverless runtime version is available
## Description
Once we resolve https://gitlab.com/gitlab-org/gitlabktl/issues/24 users will be able to use different version of the same runtime.
## Proposal
Make it possible to detect when a function is using an outdated runtime. Show "New runtime available" in the serverless tab.
/cc @danielgruesso @DylanGriffith
issue