feat(synthetics): add synthetics tests search command

[brimtown]

Summary

Wires up the SearchTests API endpoint (GET /api/v1/synthetics/tests/search) as a new pup synthetics tests search subcommand. The endpoint was already available in datadog-api-client-go but not exposed in pup — currently synthetics tests list dumps all tests with no server-side filtering.

Motivation

synthetics tests list returns all tests in an org with no filtering. The search endpoint supports facet-based queries (creator, team, env, type, etc.) making it practical to find specific tests without client-side filtering.

Changes

• Add synthetics tests search subcommand (cmd/synthetics.go) — calls datadogV1.SyntheticsApi.SearchTests with all optional parameters:
  • --text for free text and facet queries (e.g., creator:"Jane Doe", team:my-team, type:browser env:prod)
  • --facets-only to discover available facets and values for the org
  • --include-full-config to return full test configuration in results
  • --start / --count for pagination
  • --sort for result ordering
• Document all search facets with values verified against the live API: creator, team, env, type, state, status, tag, region, domain, http_method, http_path, muted, ci_execution_rule, creation_source, mobile_platform, notification, endpoint, step_count
• Update parent command help to mention search capability
• Add test (cmd/synthetics_test.go) for the new search handler

Testing

go test ./cmd -run TestRunSynthetics -v   # All pass

# Manual verification against live API
pup synthetics tests search --text='creator:"Tim Brown"' --count=5
pup synthetics tests search --text="team:applied-ai-experiences"
pup synthetics tests search --text="type:browser env:prod" --count=10
pup synthetics tests search --facets-only

Checklist

• The code change follows the project conventions
• Tests have been added/updated
• Documentation has been updated
• All CI checks pass
• Code coverage is maintained or improved