Feature request: exclude files in `search.largeFiles`

Created by: limitedmage

Feature requested by https://github.com/sourcegraph/accounts/issues/8205

Feature request description

The site config setting search.largeFiles should allow file exclusions so that known large files can be excluded from the index.

The customer has several thousand repos all with a very large file called .gitmodules (over 50,000 lines). They would like to exclude only this file and allow indexing other files.

Is your feature request related to a problem? If so, please describe.

This would be a workaround to address #40686

Describe alternatives you've considered.

• Using .sourcegraph/ignore is not feasible because the customer has several thousand repos they would need to create this file for.
• Fix #40686 or #40687

Additional context

/cc @sourcegraph/search-core