[FEA] AWS instance type picker

[lmeyerov]

Is your feature request related to a problem? Please describe.
It's not obvious which instance types support valid GPUs, so a picker would be great!

Describe the solution you'd like
A dropdown would be ideal, but unclear if formation supports.

Formation does allow specifying a restricted set of allowed values, so an option is:

• restrict to GPU types
• if not obvious in the UI, do a helpful message, like "T4: g4dn.xl (1), ..., V100: p3...."
• do for all relevant YMLs

Describe alternatives you've considered
A cloudformation parameter type:instance... but does not seem to exist