Forbid % string interpolation

[sobolevn]

As we have decided to stick to .format(), we are banning f strings: #32

But, @vergeev have also suggested to forbid 'string with %s' % some.
Here's the backstory:

• false positive S001 on modulo division gforcada/flake8-pep3101#23 has some false positives, that disallow to use regular modulo operator 5 % 2
• we can only forbid using this operator with string literals, not vars as was suggested in Forbid using f strings #32 (comment)

So, this would be valid:

some_variable % 'value1'
5 % 2

This would be invalid:

'format me %s' % 'value2'