Regex matching doesn't account for case insensitivity pattern

[tommyksander]

Note: This issue is related to recent work on:

• fix(express): dont lose route if preceded by middleware with longer path #2065
• improve express regex middleware path parsing #3203

Expected behaviour

• dd-trace should handle app.use regex strings that include case insensitivity. E.g., (/^\/(?!sample\/route).*/i)

Actual behaviour

• dd-trace doesn't identify this regex pattern, so the bug fixed in <> still exists for patterns that include case insensitivity. (code)

Steps to reproduce

• Add app.use that includes a regex with case insensitivity E.g., (/^\/(?!sample\/route).*/i)
• Run dd-trace to see routes are lost.
• Probably easiest to add this case in the unit tests and run it there: packages/datadog-plugin-express/test/index.spec.js

Environment

• Operation system:
• Node.js version:
• Tracer version:
• Agent version:
• Relevant library versions: