Document blt's flags for cuda and hip

We should add tables to our user docs/tutorial (https://llnl-blt.readthedocs.io/en/develop/tutorial/common_hpc_dependencies.html) indicating which configuration flags and variables are available/supported/expected to set up `hip` and `cuda`.

Start with the user documentation page at user docs/tutorial/common_hpc_dependencies.html and review its existing dependency guidance. Add tables that distinguish the available, supported, and expected configuration flags and variables for HIP and CUDA; the work is done when both setups are covered clearly in the tutorial.

Written by the indexing model from the issue text.