[ftr] Speed up FTR code owner check

[dolaru]

Summary

Switch to one matcher w/ all code owner patterns rather than separate matchers for each code owner pattern. Reduces the run time of scripts/check_ftr_code_owners.js by ~10x.

Before

▶ node scripts/check_ftr_code_owners.js
 info Reading CODEOWNERS file
 info Checking ownership for 8653 test files (this will take a while)
 info Ownership check complete (took 18.89 s)
 succ All test files have a code owner. 🥳

After

▶ node scripts/check_ftr_code_owners.js
 info Checked 8653 test files in 1.59s
 succ All test files have a code owner 🥳

[jbudz]

packages/kbn-test/index.ts

[elasticmachine]

💛 Build succeeded, but was flaky

• Buildkite Build
• Commit: f84e7b8

Failed CI Steps

• Jest Tests #10
• FTR Configs #73

Test Failures

• [job] [logs] Jest Tests #10 / EQL Tab rendering should render the timeline table
• [job] [logs] FTR Configs #73 / serverless search UI Serverless Inference Management UI delete action "before each" hook for "deletes modal successfully with usage"

Metrics [docs]

✅ unchanged

cc @dolaru