Implement the Ingress support to configurate an ACME issuer

[lonelyCZ]

Fixes #39

[lonelyCZ]

/assign @irbekrm

[irbekrm]

Thank you @lonelyCZ this is really good work.

I have tested this on a GKE cluster by pre-creating a static IP address and passing it as controller.service.loadBalancerIP as well as setting up DNS and passing a custom hostname and email- the Certificate became ready and I verified that the ingress backend is configured with the newly issued cert:

irbe@testing-addons$ k get cert,cr -A
NAMESPACE      NAME                                            READY   SECRET              AGE
ingress-demo   certificate.cert-manager.io/ingress-test-cert   True    ingress-test-cert   16m

NAMESPACE      NAME                                                         APPROVED   DENIED   READY   ISSUER           REQUESTOR                                         AGE
ingress-demo   certificaterequest.cert-manager.io/ingress-test-cert-fxcwg   True                True    ingress-issuer   system:serviceaccount:cert-manager:cert-manager   16m

irbe@cm-ingress$ kubectl ingress-nginx certs --host <redacted-hostname> -n ingress-nginx | openssl x509 -text -noout | grep Issuer
        Issuer: C = US, O = (STAGING) Let's Encrypt, CN = (STAGING) Artificial Apricot R3
                CA Issuers - URI:http://stg-r3.i.lencr.org/

Again, great work and thanks for updating the Readme!

/lgtm

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