Adjust the MR approval rule to use a smaller modal

Issue: #204803 (closed)

What does this MR do?

Adjust the modal size to utilize the original small size (and NOT the default medium size).

Testing Case

For an idea how small should look like, see here > https://gitlab-org.gitlab.io/gitlab-ui/?path=/story/base-modal--default

Project Settings Page

1. Go to the Project Settings Page > Expand Merge request approvals
2. Click on "Add approval rule"

• The modal size is "small"

3. Click on "Edit"

• The modal size is "small"

MR Edit Page

1. Go to a Merge Request Page > Click Edit
2. Click on "Add approval rule"

• The modal size is "small"

3. Click on "Edit"

• The modal size is "small"

Screenshots

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

Closes #204803 (closed)