Add action to deployment

What does this MR do?

In https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/22380, we made Deployment stateful object, today you can check the deployment status, however, you have no idea if the deployment action is for starting environment or stopping environment.

Deployment should have a column action which represents the deployment action is for starting or stopping.

NOTE: We will not start using this value from this MR, but in the future release. To avoid the huge migration in the feature, we should start recording the value now, rather than later.

This idea was originally proposed by @ayufan

What are the relevant issue numbers?

Related: https://gitlab.com/gitlab-org/gitlab-ce/issues/25140

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• [-] Documentation created/updated
• Tests added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• [-] Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.