Protect commits/:sha from many Gitaly timeouts

What does this MR do?

The GET /api/:version/repos/:namespace/:project/commits/:sha endpoint can receive many requests from Jira for the same sha which timeout #331326 (comment 644591676).

This is causing a noticeable latency spike on the endpoint.

Because certain SHAs reliably fail to return data #331326 (comment 641526740) and are frequently hit #331326 (comment 644591676), this change has the endpoint return an empty set of diff files for a day rather than continue to call Gitaly.

This will alleviate the endpoint from latency problems while we do an expected longer look into the underlying problem gitaly#3741 (closed).

#331326 (closed)

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?)
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• [-] 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.

Related to #331326 (closed)