Add handling for Traefik v2 acme.json

Description

This PR essentially adds the possibility to handle acme.json files generated by Traefik v2.

Traefik v2 adds the concept of multiple certificate resolvers (reference). As such, the structure of acme.json is slightly different.

Old acme.json from Traefik v1:

{
  "Account": {
    "Email": "someone@example.com",
    "Registration": {
      "body": {
        "status": "valid",
        "contact": [
          "mailto:someone@example.com"
        ]
      },
      "uri": "https://acme-v02.api.letsencrypt.org/acme/acct/<redacted>"
    },
    "PrivateKey": "<redacted>",
    "KeyType": "4096"
  },
  "Certificates": [
    {
      "Domain": {
        "Main": "example.com",
        "SANs": null
      },
      "Certificate": "<redacted>",
      "Key": "<redacted>"
    }
  ...
  ]
}

New acme.json from Traefik v2:

{
  "default": {
    "Account": {
      "Email": "someone@example.com",
      "Registration": {
        "body": {
          "status": "valid",
          "contact": [
            "mailto:someone@example.com"
          ]
        },
        "uri": "https://acme-v02.api.letsencrypt.org/acme/acct/<redacted>"
      },
    "Certificates": [
      {
        "domain": {
          "main": "example.com",
          "sans": [
            "sub.example.com"
          ]
        },
        "certificate": "<redacted>",
        "key": "<redacted>",
        "Store": "default"
      }
    ...
    ]
  }
}

Note the top-level "default" object (which is the name of the certificate resolver), as well as changed capitalization on Domain, Main, Certificate etc.

In order to support this file, I basically copied dumpcerts.acme.v2.sh, adapted it to this structure, and added detection in certs_helper.sh.

Type of change

[x] New feature (non-breaking change which adds functionality)

Status

[x] Ready
[ ] In development
[ ] Hold

How has this been tested ?

I use this in production with on my own instance using Traefik v2 - so far it works well. However, I don't use wildcard certificates, so I haven't been able to test functionality with wildcard certificates.

[x] Non-Wildcard certificate
[ ] Wildcard certificate

hardware / mailserver