Deprecation of ECX Resources

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](https://docs.github.com/en/get-started/writing-on-github/getting-started-with-writing-and-formatting-on-github/basic-writing-and-formatting-syntax#alerts) 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 https://github.com/equinix/terraform-provider-equinix/issues/462