releases.hashicorp.com is no longer served through Fastly

[apparentlymart]

The docs about the Terraform Cloud agent currently mention under [Networking Requirements(https://developer.hashicorp.com/terraform/cloud-docs/agents/requirements#networking-requirements) the implementation detail that releases.hashicorp.com is served through Fastly's CDN:

Additionally, the agent must also be able to communicate with any services required by the Terraform code it is executing. This includes the Terraform releases distribution service, releases.hashicorp.com (supported by Fastly), as well as any provider APIs. [...]

At the time of writing, releases.hashicorp.com is no longer served through Fastly's CDN, so this statement is inaccurate and linking to Fastly's IP ranges documentation is misleading.

We'll need to decide here whether to change this documentation to describe the new implementation detail of which CDN this uses, or alternatively to remove the mention of this implementation detail altogether if we don't wish to promise we'll be using our current CDN provider forever.