Add "change made by", "peer reviewed by" and "merged by" to the Compliance Dashboard

What does this MR do?

This MR adds the "Change made by", "Peer review by" and "Merged by" sections as well as unifying the user avatar sizes across the whole drawer.

To do this, this MR updates the backend to pass the correct data through and creates some new components to render the new sections. As well as building out the shared components to keep the drawer DRY.

This MR also updates the documentation to keep it current.

Screenshots (strongly suggested)

Screen_Recording_2021-07-09_at_08.11.04

Default	Lots of commenters	No content	Partial content

Setup & testing

This requires a GitLab Ultimate license to use

1. Enable the feature flag: echo "Feature.enable(:compliance_dashboard_drawer)" | rails c
2. Go to [HOST]/groups/[GROUP]/-/security/compliance_dashboard
3. Check that MR's are shown, if they aren't then you may need to merge some in the group
4. Check the MR's reviewer data appears in the drawer and links to the correct user
5. Check that all the user avatars are the same size

Does this MR meet the acceptance criteria?

Conformity

• I have included changelog trailers, or none are needed. (Does this MR need a changelog?)
• I have added/updated documentation, or it's not needed. (Is documentation required?)
• I have properly separated EE content from FOSS, or this MR is FOSS only. (Where should EE code go?)
• I have added information for database reviewers in the MR description, or it's not needed. (Does this MR have database related changes?)
• I have self-reviewed this MR per code review guidelines.
• This MR does not harm performance, or I have asked a reviewer to help assess the performance impact. (Merge request performance guidelines)
• I have followed the style guides.
• This change is backwards compatible across updates, or this does not apply.

Availability and Testing

• I have added/updated tests following the Testing Guide, or it's not needed. (Consider all test levels. See the Test Planning Process.)
• I have tested this MR in all supported browsers, or it's not needed.
• I have informed the Infrastructure department of a default or new setting change per definition of done, or it's not needed.

Security

Does this MR contain changes to processing or storing of credentials or tokens, authorization and authentication methods or other items described in the security review guidelines? If not, then delete this Security section.

• [-] 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 #331263 (closed)