Add docs for sample RQD CUDA Dockerfile

[n-jay]

Link the issue(s) this pull request is related to. Related to OpenCue PR #1327 as discussed here.

Summarize your change. Adds new Sample Dockerfiles section to the Customizing RQD page and appends the CUDA Dockerfile docs as a subsection. Also converts the existing Reviewing a sample Dockerfile section to a subsection within Sample Dockerfiles for a better flow.

Keeping PR as a draft until the Dockerfile gets finalized.

[n-jay]

Ping @bcipriano