feat: Bump a major version and require bleach>6.0.0

The code in this repo has been updated to work with bleach 6.0.0 and
will break with older versions so make that dependency clear in base.in
and do a major version update.

lti_consumer/__init__.py

@@ -4,4 +4,4 @@ Runtime will load the XBlock class from here.
 from .apps import LTIConsumerApp
 from .lti_xblock import LtiConsumerXBlock
 
-__version__ = '7.3.0'
+__version__ = '8.0.0'

requirements/base.in

@@ -3,7 +3,7 @@
 
 attrs
 lxml
-bleach
+bleach>=6.0.0
 django
 oauthlib
 mako