feat(securitycenter): Add Resource SCC Management API Org ETD Custom Module samples (GetEff, ListEff, ListDesc, Validate)

[vijaykanthm]

Description

Fixes b/347347198, b/347347148, b/347346945, b/347347455
This PR adds SCC Managament API Org ETD Custom Module Samples to GetEff, ListEff, ListDesc, & Validate.

Note: Before submitting a pull request, please open an issue for discussion if you are not associated with Google.

Checklist

• I have followed Contributing Guidelines from CONTRIBUTING.MD
• Tests pass: go test -v ./.. (see Testing)
• Code formatted: gofmt (see Formatting)
• Vetting pass: go vet (see Formatting)
• These samples need a new API enabled in testing projects to pass (let us know which ones)
• These samples need a new/updated env vars in testing projects set to pass (let us know which ones)
• This sample adds a new sample directory, and I updated the CODEOWNERS file with the codeowners for this sample
• This sample adds a new Product API, and I updated the Blunderbuss issue/PR auto-assigner with the codeowners for this sample
• Please merge this PR for me once it is approved

[conventional-commit-lint-gcf]

🤖 I detect that the PR title and the commit message differ and there's only one commit. To use the PR title for the commit history, you can use Github's automerge feature with squashing, or use automerge label. Good luck human!

-- conventional-commit-lint bot
https://conventionalcommits.org/

[snippet-bot]

Here is the summary of changes.

You are about to add 4 region tags.

• securitycenter/management_api/event_threat_detection/get_effective_event_threat_detection_custom_module.go:17, tag securitycenter_get_effective_event_threat_detection_custom_module
• securitycenter/management_api/event_threat_detection/list_descendant_event_threat_detection_custom_module.go:17, tag securitycenter_list_descendant_event_threat_detection_custom_module
• securitycenter/management_api/event_threat_detection/list_effective_event_threat_detection_custom_module.go:17, tag securitycenter_list_effective_event_threat_detection_custom_module
• securitycenter/management_api/event_threat_detection/validate_event_threat_detection_custom_module.go:17, tag securitycenter_validate_event_threat_detection_custom_module

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