Update CI/CD Documentation for AWS Secrets Manager

Description

Create comprehensive documentation for the AWS Secrets Manager integration in GitLab CI/CD, helping users understand how to configure and use this feature in their pipelines.

Goals

• Document the AWS Secrets Manager integration in GitLab CI/CD
• Provide clear configuration examples and parameter descriptions
• Explain integration with existing CI/CD features
• Add troubleshooting guidance

Implementation Plan (Brief Overview)

1. Identify appropriate locations to add documentation
2. Create documentation for AWS Secrets Manager configuration
3. Add examples for common use cases
4. Include troubleshooting guidance
5. Update relevant existing documentation to reference AWS Secrets Manager

Documentation should include:

# AWS Secrets Manager integration

GitLab CI/CD integrates with AWS Secrets Manager, allowing you to securely
retrieve secrets during pipeline execution.

## Configuration

To use AWS Secrets Manager in your pipeline, configure the `secrets` section
in your `.gitlab-ci.yml` file:

```yaml
job_name:
  id_tokens:
    AWS_TOKEN:
      aud: https://gitlab.com
  secrets:
    DATABASE_PASSWORD:
      aws_secret_manager:
        name: my-database-password
        region: us-east-1
      token: $AWS_TOKEN
  script:
    - echo "Using database password from AWS Secrets Manager"
    - my-application --password $DATABASE_PASSWORD
```

Required parameters

• name: Name of the secret in AWS Secrets Manager
• region: AWS region where the secret is stored

Optional parameters

• version_id: Specific version ID of the secret
• version_stage: Version stage label (e.g., AWSCURRENT)
• file: Whether to store the secret as a file (default: true)

Testing Plan

1. Follow documentation to set up a test pipeline
2. Verify all examples work as documented
3. Test troubleshooting guidance against common issues
4. Review for clarity, accuracy, and completeness

Acceptance Criteria

• Documentation clearly explains AWS Secrets Manager integration
• Configuration examples are accurate and work as described
• Parameter descriptions are complete and accurate
• Documentation follows GitLab documentation standards
• Documentation is reviewed and approved by technical writers

Dependencies

• Define and Implement AWS Secrets Manager Schema