Limit rendering of commit messages

What does this MR do?

Applies a 1MiB limit to the source of commit messages when they are passed through banzai

Commit messages can be of arbitrary size, and banzai rendering is expensive. Further, we often render large number of commit messages at a time, via commit list views.

Limiting to 1MiB mirrors issuable limits and should be enough to avoid having these pages time out due to a batch of very long commit messages. Right now, we terminate rendering after 1 minute, which is suboptimal.

Screenshots (strongly suggested)

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 #292039 (closed)