Move ingress rewrite to dashboard Nginx

[migmartri]

Based on this discussion #897 (review) I've managed to extract the redirection logic to the Nginx configuration inside the dashboard container as well as made it generic. This is good since now, the redirect does not depend now on the specifics of the Ingress controller as well as the deployment mechanism (Helm chart).

In my previous tests the solution did not work because the redirection was including the internal port (8080)

NOTE: see location header in the following examples.

$ curl -I -H 'Cache-Control: no-cache' https://miguel-kubeapps-dev.k.dev.bitnami.net/kubeapps
HTTP/2 301 
server: nginx/1.15.6
date: Wed, 02 Jan 2019 21:16:01 GMT
content-type: text/html
content-length: 185
location: http://miguel-kubeapps-dev.k.dev.bitnami.net:8080/kubeapps/

I tried disabling the port via the directive port_in_redirect off; but that made the internal server_name to be shown. Adding also server_name_in_redirect did not help either.

$ curl -I -H 'Cache-Control: no-cache' https://miguel-kubeapps-dev.k.dev.bitnami.net/kubeapps
HTTP/2 301
server: nginx/1.15.6
date: Wed, 02 Jan 2019 21:18:43 GMT
content-type: text/html
content-length: 185
location: http://miguel-kubeapps-internal-dashboard/kubeapps/

Setting the redirects relative does the trick.

$ curl -I -H 'Cache-Control: no-cache' https://miguel-kubeapps-dev.k.dev.bitnami.net/kubeapps
HTTP/2 301 
server: nginx/1.15.6
date: Wed, 02 Jan 2019 21:14:43 GMT
content-type: text/html
content-length: 185
location: /kubeapps/

Refs #402

[prydonius]

this is great, thanks. Also fixes the current broken chart when path = /

[prydonius]

Merging due to the current broken chart.