Limit number of shown environments

## What does this MR do?

This MR limits in context of Merge Request a list of shown environments. Previously we would show all environments containing the SHA of the head commit of Merge Request. However, with introducing of dynamically created environments this lead to a cases that we would show multiple review apps, for different branches, because these branches would contain a new questioned commit.

This MR changes what environments we test against presence of the commit, to:
1. We look for environments with deployments to source_branch of source_project: used for deployments to per-branch environments,
2. We look for environments with deployments to target_branch of target_project: used for deployments to staging / production environments,
3. We look for environments with deployments for tags on target_project: used for staging / production environments.

## Why was this MR needed?

To improve a list of returned environments when we introduced ability to create dynamic environments for review apps:
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/6323

See merge request !6438