[website/doc] integrations: Enhance Apache Guacamole integration how to login with selfsigned CA

[cheggerdev]

Describe the solution you'd like
Enhance Apache Guacamole integration with information how to successfully login with self-signed CA.

Additional context
If using a selfsigned Certificate with a self-signed CA then login with OpenID fails because the JWT validation of the authentik token fails and is rejected in consequence.
The solution is to add your CA to both /etc/ssl/certs/ca-certificates.crt and to /opt/java/openjkd/jre/lib/security/cacerts

Here is how to do the latter part:
openssl pkcs12 -export -in yourCA.crt -inkey yourCA.key -out yourCA.p12 -passout pass:something
keytool -importkeystore -srckeystore yourCA.p12 -srcstoretype PKCS12 -keystore /opt/java/openjdk/jre/lib/security/cacerts -deststorepass changeit -nopromt -srcstorepass something