Scale canary deployments
### Description
With https://gitlab.com/gitlab-org/gitlab-ce/issues/38543 you can scale your deployments using the **CI/CD > Environments** page. If you use canary deployments, you should be able to do the same.
### Proposal
Implement a flow to scale canary deployments from the **CI/CD > Environments** page.
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### Design
The design is from https://gitlab.com/gitlab-org/gitlab-ee/issues/5416
The labels and all the copying should be revisited to adapt to this new scope.

*(TODO: Where is the documentation links to?)*
##### Tooltips
It has the short help text in a tooltip to explain the terms of `Instances` and `Incremental rollouts`.
*(Note: the copy is not ready yet.)*

issue