web-ui: enable provided ssl keystore

[sven-dmlr]

Situation

Currently Nginx always uses a self-signed certificate created along with the container build.

Wanted

Possibilty to provide a custom ssl key and certificate.
In the first step pkcs12 keystore format shall be supported (because it is already used in SecHub server).

Solution

Create a "certificate management script" for the container which checks if a custom pkcs12 keystore is provided.
If yes then the script replaces the self-signed with the custom ones from the pkcs12 file.