fix: Disable backslash escapes

[mfranczel]

Part of PLA-3983

Todos

• MIT compatible
• Tests
• Documentation
• Updated CHANGES.rst

[OlegWock]

Changes here doesn't seem to target specific sqlalchemy version, are they backward compatible with older versions of sqlalchemy we support?

[mfranczel]

@OlegWock It should be compatible with older sqlalchemy versions - issue with the new one was that 2.0 by default calls SHOW standard_conforming_strings which is not supported by redshift, causing it to error out. Disabling backslash escapes in the dialect tells sqlalchemy to skip it. So:

• sqlalchemy < 2 doesn't call it altogether no matter what we set here
• sqlalchemy >= 2 would call it by default, unless it's specified in dialect that it's not supported