refactor: move `config/samples/` to `examples/` and add docs

[zyy17]

What's changed

1. Move config/samples to examples and refine the naming of the directory;
2. Don't specify namespace field in the examples(let the users decide the namespace);
3. Remove unnecessary license header;
4. Add README.md for examples/;

Summary by CodeRabbit

Release Notes

• New Features

  • Introduced various configurations for deploying GreptimeDB clusters, including support for AWS NLB, GCS, OSS, S3, and TLS.
  • Added examples for deploying standalone instances of GreptimeDB with GCS, OSS, and S3 integration.
  • Integrated Prometheus monitoring capabilities for GreptimeDB clusters.

• Bug Fixes

  • Removed outdated configurations that could impact deployments relying on specific storage solutions and setups.

• Documentation

  • Added comprehensive README files with examples for using the GreptimeDB Operator, enhancing user guidance for various configurations.