Use embedded Flux manifests for air-gapped bootstrap

[stefanprodan]

This PR allows running bootstrap in air-gapped environments by embedding the Flux manifests in the provider binary.

Description

With embedded_manifests enabled and registry set to an private container registry where the Flux images are copied, users can run bootstrap on air-gapped environments where access to GitHub is denied.

Tip

All users should enable embedded_manifests instead of setting version, this not only reduces the network traffic but also ensures that the Flux deployment matches the provider version.

Motivation and Context

The implementation in #503 has many flaws, the major problem is that customisations no longer work and users have to download the manifest files by hand before running bootstrap.

Fix: #590
Fix: #634

How has this been tested?

• Have you added an acceptance test for the functionality being added?
• Have you run the acceptance tests on this branch?

Manually tested with github.com dropped in firewall.

resource "flux_bootstrap_git" "this" {
  path = "clusters/air-gapped"
  embedded_manifests = true
  registry = "docker.io/fluxcd"
}

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

• I have updated the documentation (if required) with make docs

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I've read the CONTRIBUTION guide
• I have signed-off my commits with git commit -s

[swade1987]

This whole section should be in the documentation that gets rendered on the Terraform registry.

With embedded_manifests enabled and registry set to an private container registry where the Flux images are copied, users can run bootstrap on air-gapped environments where access to GitHub is denied.

Tip
All users should enable embedded_manifests instead of setting version, this not only reduces the network traffic but also ensures that the Flux deployment matches the provider version.

[stefanprodan]

This whole section should be in the documentation that gets rendered on the Terraform registry.

Which one is that, haven't you deleted all guides? Better to have this here https://fluxcd.io/flux/installation/configuration/air-gapped/