Rename /interfaces to /integrations

Done

rename /interfaces/<interface-name> to /integrations/<interface-name>
redirect from /interfaces/<interface-name> to /integrations/<interface-name>
How to QA
Go to https://charmhub-io-1817.demos.haus and click on any charm that has integrations examples are: kafka, kafka-k8, prometheus, click on the charm's integration tab, then click on any interface, ensure that it redirects to /integrations/<interface-name>
Go to https://charmhub-io-1817.demos.haus/integrations/grafana_dashboard and ensure that it shows as expected, compare to production. Repeat for any other interface of your choice and ensure it works as expected.
Go to https://charmhub-io-1817.demos.haus/interfaces/interface-name and ensure it redirects to integrations/<interface-name>
Issue / Card https://warthogs.atlassian.net/browse/WD-10961

Fixes #