[stable/traefik] ACME wildcard certificate support

[farfeduc]

Is this a request for help?:
Yes

FEATURE REQUEST:
I want support of wildcard certificates as described in traefik documentation here : https://docs.traefik.io/v1.6/configuration/acme/#wildcard-certificates
I think the modifications are not that complicated (bump traefik version + add optional values in configmap template).

Version of Helm and Kubernetes:
Helm v2.9.0
Kubernetes v1.9.6
On-premise install

Which chart:
stable/traefik

What you expected to happen:
Be able to set the acme.domains.main option as detailled in traefik 1.6 documentation for wildcard certificate generation.

Anything else we need to know:
I have done a fork : https://github.com/farfeduc/charts with some modification that might resolve the issue but as I created a new pull request I became overwhelmed with the requirements.
So instead I thought it would be better to fill an issue with some work already done to ask if my modifications are correct.

@krancour If you have some time I would really appreciate some pointers on what I might have done wrong 😄 Thanks in advance.

[krancour]

@farfeduc I made a few comments on the last commit to your fork.