Rename plugin options to be consistent across the hapi ecosystem

[spridev]

The hapi ecosystem offers the following official authentication plugins:

• basic: uses validate and isValid (reference)
• jwt: uses validate and isValid (reference)
• cookie: uses validateFunc and valid (reference)
• bell: does not use a validation function

This merge request aims to make these options consistent across all plugins.

[devinivy]

This is going into a branch for v12. Thanks!