CSPL-3156: Add `kubectl-splunk` Plugin for Executing Splunk Commands within Kubernetes Pods

[vivekr-splunk]

Description

This pull request introduces comprehensive support for the Splunk plugin within kubectl, enabling seamless interaction and management of Splunk instances deployed in Kubernetes clusters. The enhancements include:

• Plugin Functionality: Allows execution of Splunk CLI commands, REST API interactions, file operations, and interactive shell access directly from kubectl.
• Authentication Handling: Implements secure credential storage and automatic retrieval of Splunk admin credentials from pods.
• Configuration Management: Supports configuration via files, environment variables, and command-line arguments for flexibility and ease of use.
• User Experience Enhancements: Adds verbosity levels, caching mechanisms for pod information, and auto-completion support to improve usability.
• Documentation: Updates the README.md to provide detailed usage instructions, examples, and configuration guidelines.
• Testing: Includes unit tests to ensure reliability and correctness of the plugin's functionalities.
• License Update: Apache License 2.0 to align with project requirements.

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Related Issue

Closes CSPL-3156

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Type of Change

• New Feature
  Introduces new functionalities to support Splunk operations within kubectl.

• Documentation Update
  Enhances the README.md with detailed instructions, examples, and license information.

• License Change
  Updates the project license to Apache License 2.0.

• Testing
  Adds unit tests to cover the new features and ensure code reliability.

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How Has This Been Tested?

• Unit Tests
  Implemented using Python's unittest framework with unittest.mock for isolating components. All tests pass successfully, ensuring that new functionalities work as intended.

  python -m unittest discover -s tests

• Manual Testing
  Performed manual verification of all plugin modes (exec, rest, cp, interactive) to ensure they function correctly within a Kubernetes cluster with Splunk deployments.

• PyPI Deployment
  Uploaded the package to PyPI and verified installation and functionality using pip and pipx.

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Checklist

• [x] Code follows the project’s style guidelines.
• [x] Performed a self-review of my own code.
• [x] Commented code, particularly in hard-to-understand areas.
• [x] Made corresponding changes to the documentation (README.md).
• [x] Added tests that prove my fix is effective or that my feature works.
• [x] New and existing unit tests pass locally with my changes.
• [x] Updated the LICENSE file to Apache License 2.0.
• [x] Necessary badge updates in README.md reflecting the license change.

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License

This project is now licensed under the Apache License 2.0. Please see the LICENSE file for details.

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Additional Information

• Configuration File Location: ~/.kubectl_splunk_config
• Credentials File Location: ~/.kubectl_splunk_credentials
• Cache File Location: /tmp/kubectl_splunk_cache.json
• Supported Python Versions: 3.6 and above
• Shell Auto-Completion: Supports bash and zsh via argcomplete