feat!: add ingress_per_unit integration to glauth-k8s-operator

[NucciTheBoss]

Same as PR #78 but with recovered commits + removed merge commit.

This PR adds the ingress_per_unit integration to glauth-k8s so that the glauth TCP service can be addressable from machine charms outside of the Kubernetes cluster. Now, when a machine charm wants to connect to glauth for LDAP goodness, all you need to do is integrate glauth-k8s with traefik:

# Enable LoadBalancer implementation for your k8s cloud.
# In testing I used MetalLB with an IPADDR range partitioned off of my bridged LXD network.
microk8s enable metallb:<IPADDR range>  # Can also use Canonical k8s.

# Do the necessary setup by integrating with `postgresql-k8s` and `self-signed-certificates`...
juju deploy glauth-k8s --trust
juju deploy traefik-k8s --trust
juju integrate glauth-k8s:ingress traefik-k8s
# glauth TCP endpoint will be proxied by traefik and reachable from machine charms such as SSSD.

Breaking changes

One thing to note is that I updated the function signature of the ldap_url to return List[str] instead of str. I don't think it's that much of an issue as ldap_url is only used two times within the operator, and its returned value was casted to List[str] to satisfy the type requirements for the urls field in the ldap interface.

Related issues

• Fixes Ingress enablement for GLAuth charm  #76

[NucciTheBoss]

@shipperizer @wood-push-melon this PR is the same thing as #78 but restores the clobbered commits. Accidentally knee-capped the original branch when I removed the merge commit from main. Has the recommended changes suggested such as a FIXME comment about the traefik-k8s sacling issue, integration name declared in constants, and the rename of ldap_url to ldap_urls.