Deprecation of ECX Resources

[displague]

ECX APIs are deprecated and will be EOL'd in early 2024.

In light of that, this project should take one of the following approaches:

• replace ECX resources with Fabric v4 resources
  https://registry.terraform.io/providers/equinix/equinix/latest/docs/guides/migration_guide_fabricv3_to_fabricv4
  (preferred approach for illustrative modules that intend to model Fabric resource usage)

• adopt a Fabric module that abstracts the provider resources away:
  https://registry.terraform.io/modules/equinix/fabric/equinix/latest (see Submodules and Examples)
  (preferred approach for modules that do more than connect Fabric to another provider, constructing a complex configuration)

• EOL this module in favor of the equivalent module or example from above
  (preferred approach for modules that only connect Fabric to another provider)

  EOL steps:

  • Update the GH About title with the prefix: "DEPRECATED: " and change the URL to the refer to the replacement example or submodule
  • Update any lifecycle badges in README.md to EOL and add a note about the project being deprecated. https://github.com/equinix/terraform-provider-metal?tab=readme-ov-file#equinix-metal-terraform-provider may serve as an example.
  • Close any open issues with a comment referring a comment in this issue confirming the approach taken
  • Archive the module in GH settings

Related to equinix/terraform-provider-equinix#462