docs: Remove experimental verbiage from Ephemeral Resources

[austinvalle]

Module version

v1.13.0 (not yet released)

Proposal

#1050 introduces experimental support for ephemeral resource types, which will first be available in beta releases for Terraform v1.10. Once Terraform v1.10 goes GA, we can remove the experimental call outs in the website documentation and Go package docs.

Depending on if we have other functionality to release, we can do this in a patch or minor version release.