feat(cluster): add FluxCD env creation during agent bootstrap

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Description

This merge request implements FluxCD environment creation during the GitLab agent bootstrap process. The changes provide a seamless integration for setting up FluxCD environments alongside the agent installation.

• feat(cluster): add FluxCD environment creation during agent bootstrap

• Add --create-flux-environment flag (defaults to true) to create environment for FluxCD
• Add configuration flags for FluxCD environment name, namespace and resource path
• Refactor environment configuration to support both agent and FluxCD environments
• Update bootstrap command to handle FluxCD environment setup

Fixes #7720 (closed)

• docs: Adding snapcraft info

Related Issues

Resolves #[7720]

How has this been tested?

• Tested agent bootstrap with FluxCD environment creation enabled and disabled
• Verified environment creation with different configuration parameters
• Tested in both new and existing cluster setups
• Verified proper error handling and validation
• Tested integration with existing agent bootstrap functionality
• Ran full test suite including new integration tests

Testing environments:

• Local Kubernetes cluster (kind v0.20.0)
• GitLab Enterprise Edition 16.11
• FluxCD v2.2.0

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation
• Chore (Related to CI or Packaging to platforms)
• Test gap

Closes #7720 (closed)