[Policy tests] Use go-ucfg to read policy test configuration files

[mrodm]

As skip configuration is set with tags config, those settings were ignored when reading the policy test configuration. This caused that policy tests could not be skipped.

This PR updates the method to read the configuration to use go-ucfg and go-ucfg/yaml libs. This is the same approach done for pipeline and system tests.

Example

### Current elastic-package version 0.120.0
 $ elastic-package-v0.120.0 test policy -C test/packages/parallel/httpcheck 
Run policy tests for the package
2026/02/20 13:45:43  INFO elastic-package v0.120.0 version-hash 97620231 (build time: 2026-02-18T17:17:16+01:00)
2026/02/20 13:45:43  INFO elastic-stack: 9.4.0
--- Test results for package: httpcheck - START ---
╭───────────┬─────────────┬───────────┬───────────────────┬────────┬───────────────╮
│ PACKAGE   │ DATA STREAM │ TEST TYPE │ TEST NAME         │ RESULT │  TIME ELAPSED │
├───────────┼─────────────┼───────────┼───────────────────┼────────┼───────────────┤
│ httpcheck │             │ policy    │ test-eprcheck.yml │ PASS   │ 12.894671393s │
│ httpcheck │             │ policy    │ test-skip.yml     │ PASS   │  9.005140439s │
╰───────────┴─────────────┴───────────┴───────────────────┴────────┴───────────────╯
--- Test results for package: httpcheck - END   ---

### Changes in this Pull Request

 $ elastic-package test policy -C test/packages/parallel/httpcheck 
Run policy tests for the package
2026/02/20 13:47:01  INFO elastic-package v0.120.1-0.20260219114940-03f307bc3057+dirty version-hash 03f307bc-dirty (build time: 2026-02-20T13:35:56+01:00)
2026/02/20 13:47:01  INFO elastic-stack: 9.4.0
2026/02/20 13:47:14  WARN skipping policy test for httpcheck/: Test skipped tests (details: https://github.com/elastic/elastic-package/pull/1)
--- Test results for package: httpcheck - START ---
╭───────────┬─────────────┬───────────┬───────────────────┬─────────────────────────────────────────────────────────────────────────────────┬───────────────╮
│ PACKAGE   │ DATA STREAM │ TEST TYPE │ TEST NAME         │ RESULT                                                                          │  TIME ELAPSED │
├───────────┼─────────────┼───────────┼───────────────────┼─────────────────────────────────────────────────────────────────────────────────┼───────────────┤
│ httpcheck │             │ policy    │ test-eprcheck.yml │ PASS                                                                            │ 11.769181203s │
│ httpcheck │             │ policy    │ test-skip.yml     │ SKIPPED: Test skipped tests [https://github.com/elastic/elastic-package/pull/1] │     169.388µs │
╰───────────┴─────────────┴───────────┴───────────────────┴─────────────────────────────────────────────────────────────────────────────────┴───────────────╯
--- Test results for package: httpcheck - END   ---
Done

Author's checklist

• Include a policy test that should be skipped
• Test with packages in integrations repository: https://buildkite.com/elastic/integrations/builds/38575

How to test this PR locally

Add to a policy test the following configuration:

skip:
  reason: This test is flaky and needs to be fixed.
  link: https://github.com/elastic/elastic-package/issues/1

Execute elastic-package policy test and this test should be skipped.

Screenshots

[mrodm]

test integrations

[elastic-vault-github-plugin-prod]

Created or updated PR in integrations repository to test this version. Check elastic/integrations#17493

[mrodm]

/test

[elasticmachine]

💛 Build succeeded, but was flaky

• Buildkite Build
• Commit: 3a59884

Failed CI Steps

• :windows: Run stack tests

History

• 💔 Build #7232 failed 3a59884
• 💚 Build #7231 succeeded 706f4d2
• 💔 Build #7230 failed fb25870

cc @mrodm