Adding initial tracking for file size highlight limits [RUN ALL RSPEC] [RUN AS-IF-FOSS]

What does this MR do?

GitLab will only highlight text if it is under a certain file size. The default value is 512kb, but that can be configured in the gitlab.yml file. (see: !60445 (merged) )

For #31065, we are trying to decide if that is the best number to have as a default. To figure that out, we need some metrics:

This MR will introduce a feature flag track_file_size_over_highlight_limit that, when enabled, will increment a metric each time we go over the file size configured in Gitlab.config.extra['maximum_text_highlight_size_kilobytes'].

Screenshots (strongly suggested)

Does this MR meet the acceptance criteria?

Conformity

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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
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Security

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• 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
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Related to #31065