openapi3: support format conditional on `doc.openapi` version

[cboitel]

Implements string format improvements in issue #582 with openapi minor version support.

• You can now define a string formats available for some minor version
• by default, string formats apply to all minor versions (>= 3.0)
• filters do enforce string formats according to document's OpenAPI version

[cboitel]

@fenollp finally made up with implementing a string format support based on OpenAPI minor version

[fenollp]

@cboitel Hey there. Do you need help moving this forward?

[cboitel]

Nope. Just missed it while I was on vacations. Will get back to it next week.

[cboitel]

@fenollp

I had a hard time to rebase.

Finally found it was related to some new/existing tests defining string formats for uuid but not restoring string formats to original value.

I created a new Save/Restore/RestoreDefault functions for string formats so one can easily do that like we need in our tests.

I will now address your earlier comments in the upcoming days.