Validation Step for Epoch Clarified
🚀 Feature

This simple change would add the num_validation_sanity_steps flag to also include fullEpoch in addition to the synonymous -1 flag, to add clarity to the end-user.
Motivation
I grew frustrated with trying to find a way to easily run an entire validation epoch before using training loops in pytorch-lightning. After finding this parameter (#2246), I still did not like how the -1 flag works. This also confused a colleague of mine, so I decided to submit this change as a means to add clarity to the end-user.
Pitch
Allow -1 and fullEpoch flags to run the validation sanity step on an entire batch prior to training
Alternatives
Additional context
Pull Request
#3166