Support loading password credential from infinispan secret

The infinispan operator generates a secret that contains a yaml file, which is where the developer password is stored.

There three approaches:
1. for materialization assume that we will "own" the DataGrid instance such that we'll create and pass our own secret file for infinispan to use. In this case we'll know the password and can provide that to the connection factory via an env property.
2. add logic to the connection factory to specify a "credential file" such that we'll parse the yaml from the given location (a mount of the secret) and find the appropriate credential for the given username (typically developer).
3. ask the infinispan team to allow for easier consumption of the secret (a secret per user?)

To get things working with the example, I can take the first approach - but it will look a little convoluted.

In general 2 or 3 will be needed in scenarios where we expect to simply pick up existing credentials.