feat: Add ingress requirer implementation and oauth provider implementation

[Thanhphan1147]

This PR adds 2 new libraries:

1. lib/charms/hydra/v0/oauth.py which contains the oauth provider implementation
2. lib/charms/traefik_k8s/v2/ingress.py which contains the ingress requirer implementation

New relations:

ingress-v2:
    interface: ingress
    limit: 1

oauth:
    interface: oauth
    limit: 1

Ingress

The ingress library is used to integrate dex with provider charms like traefik-k8s, nginx-ingress-integrator and gateway-api-integrator, there are only 2 notable changes made in this PR:

1. The initialization of the requirer class at charm initialization
2. Update the issuer field of the dex config to reflect the ingress URL

Oauth

The oauth provider implementation is used to integrate dex with oauth requirer charm by generating a static client, add the static client to dex's config and inform the requirer of the static client via relation data.