Expand Code Review custom instruction matching pattern to accept unions

What does this MR do and why?

Expand Code Review custom instruction matching pattern to accept unions.

This change addresses the limitation observed in #517386 (comment 3386146047).

References

#517386 (comment 3386146047)

Resolves #601206 (closed)

How to set up and validate locally

You can execute the following commands in a Rails console before and after these changes and compare the differences:

instruction = Gitlab::Duo::CodeReview::CustomInstruction.new(
  name: "Name",
  include_patterns: ["**/*.{c,h}"], # <- before these changes extended globs with unions were not accepted
  exclude_patterns: [],
  location: "",
  instructions: ""
)

instruction.apply_to?("foo.c") # before: false | now: true
instruction.apply_to?("bar.h") # before: false | now: true
instruction.apply_to?("baz.d") # before: false | now: false

MR acceptance checklist

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