docs: add comparison of test functions and oauth provider table to contributing.md

[hoeseong19]

What kind of change does this PR introduce?

Docs update

What is the new behavior?

The comparison table is added to contributing.md

Additional context

There is a function (DisableSignupErrorWhen(Empty|No)Email) in the mix that tests for no(or empty) email.
It would be nice to have a choice between Empty and No.

[kangmingtay]

would prefer not to add this table since it would be an extra overhead to keep it up to date with the codebase

[hoeseong19]

Do you have any ideas of alternative to the table?
If it is decided that the comparison table will not be added, it will still be necessary to unify the names of functions.

[kangmingtay]

@hoeseong19 probably better to have a go interface that defines the different cases to test a new oauth provider

[hoeseong19]

If I do what you say, that would solve both of my problems!

I'll work on that feature and then make a new pull request.

[kangmingtay]

@hoeseong19 what are the problems you are trying to solve here? it would be great if you can create an issue first to describe the problems you face and we can discuss the solution in there before creating a PR