Set default limits for diff sizes and syntax highlighting.

Review Request #12816 — Created Jan. 30, 2023 and submitted — Latest diff uploaded


Review Board


We have options for controlling the maximum diff upload size, and for
setting the threshold of number of lines before syntax highlighting is
disabled. However, these were never given reasonable defaults.

Now, the diff upload size is set to 2MB as a default, and the syntax
highlighting is set to 20,000 lines.

These will only be set for brand-new installations. Existing installs
will retain any stored settings.

Created a new database, viewed the settings page, and saw the values.

Verified these through siteconfig debug output.