Version or additional column(s) in environment list
### Description
In order to get better overview on what and which release is currently on an environment, it would be grateful having an additional column in the environment page with the deployed version.
### Proposal
Add possibility to add additional element to the `environment` element in `.gitlab-ci.yml` like:
```
deploy:
stage: deploy
environment:
name: dev
version: $MY_VERSION
```
or
```
deploy:
stage: deploy
environment:
name: dev
metadata:
myversion1: $MY_VERSION
veryuseful: $VERYUSEFUL_INFO
```
### Links / references
### Documentation blurb
#### Overview
#### Use cases
Having fast overview of which version in which environment currently is deployed:

Maybe would this should also be displayed it would be also nice having that in the pipeline screen, when hovering of the a `deploy` stage.
### Feature checklist
Make sure these are completed before closing the issue,
with a link to the relevant commit.
- [ ] [Feature assurance](https://about.gitlab.com/handbook/product/#feature-assurance)
- [ ] Documentation
- [ ] Added to [features.yml](https://gitlab.com/gitlab-com/www-gitlab-com/blob/master/data/features.yml)
issue