Update Dev Containers docs and example templates in Coder

[bpmct]

https://coder.com/docs/v2/latest/templates/dev-containers

• Say dev containers is no longer alpha
• Add more modern examples with the envbuilder image and Terraform docs new data sources

[bpmct]

We had an internal ticket about volume expansion in the aws-devcontainer template. A one-liner can be used to expand the filesystem (as seem in ticket and AWS docs), but we also may want to reconsider our volume strategy in that template (e.g. do we really want to persist the root disk?)

[johnstcn]

A one-liner can be used to expand the filesystem (as seem in ticket and AWS docs)

It's even easier than that: https://cloudinit.readthedocs.io/en/latest/reference/modules.html#growpart