integrate with the tls certificates relation

[addyess]

This PR adds HTTPS TLS Configuration via relations to the tls-interface endpoint

There are multiple competing standards of this relation:

• legacy-tls-certificates which relates to charms like vault and easyrsa in machine models
• telco-tls-certificates which relates to the tls-certificates-operator in k8s models

Simultaneously, when one removes this relation, the charm defaults back to a SelfSignedCert

• inclusion of ops.interface-tls-certificates pypi library
• includes of tls_certificates_interface.v2.tls_certificates charm library
• unit tests

The includes on the second library makes this charm a binary specific charm needing binary specific python libraries. In order to support multiple arches, it will depend on the merge of

• https://github.com/charmed-kubernetes/jenkins/pull/1376

[addyess]

@mateoflorido would you mind re-reviewing the latest commit. I'm more satisfied with this cleanup