[Commit Page] Migrate to GlModal for revert commit

What does this MR do?

• Migrate to use GlModal from generic bootstrap modal for the Revert from a commit as rendered from app/views/projects/commit/show.html.haml

What this MR doesn't do

• handle revert from merge request, that will be handled as part of the plan in subsequent MR(s).
• handle cherry-pick from commit or merge request, that will be handled as part of the plan in subsequent MR(s).

Notable changes to UX

• cancel/revert button alignment with default pajamas - can see the difference easily by selecting cherry-pick from dropdown instead of revert
• dropdown to use pajamas version, and the look/behavior is slightly changed.

Reproducing locally(gdk)

• Go to a project and find a commit. Click into it and then use the options dropdown as seen in the screenshots below.

Screenshots (strongly suggested)

Images

action	before	after
view button
click button
show dropdown
revert click
branch in fork(can't push code)
commit to same branch with MR open(not valid for commit outside MR)

Videos

Before(ignore the failure at the end as that is a commit/local issue)

Screen_Recording_2020-12-30_at_6.42.32_PM

After

Screen_Recording_2020-12-30_at_4.46.27_PM

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team

Related to #229679