Deprecate ecx-go

[displague]

ECX Go is a hand-maintained SDK managed by Equinix employees and the community of users. This SDK has been used by Equinix users and developers for various integrations including the Equinix Terraform Provider.

With the launch of Equinix Fabric v4 APIs and the deprecation of ECX v2 and v3 APIs, this package is showing its age. Additionally, the scope of services offered by Equinix Fabric has expanded beyond the rate of contributions to this repo.

The Equinix Fabric API's published API Spec has been evolving in this time. It is now ready to be used in generated SDKs and those SDKs are proving ready for integrations like Terraform. This ecx-go project was initially create for Terraform use only and the project has been messaged as such (README.md) to prevent further adoption.

Fabric Go is the successor to ECX Go and is being used today to build the Equinix Fabric Terraform resources.

equinix/terraform-provider-equinix#112
equinix/terraform-provider-equinix#445

• add Deprecated to project settings description
• add Deprecation notice and badge https://github.com/equinix-labs/equinix-labs/blob/main/deprecated-statement.md, referring users to fabric-go
• add Go deprecation comments to the package https://go.dev/ref/mod#go-mod-file-module-deprecation
• Review / Resolve open PRs
• Archive the project