Implement ability to read parameter from yaml files

[ahelmbr]

Add ability to read all information from yaml file(s) - this could be a single parameter or a block of parameters or at least the whole command could be packed into a yaml file and read from there:

Identifier for reading from File is @
examples:
mqtt con -u @myname.yaml
mqtt @myFile.yaml

Content should look like described in the example:

mqtt:
_version: 5
method: con
client:
identifier: C1
user: Max
password: "$"
cleanStart: 1
sessionExpiry: 0
will:
properties:
p:
- "p1:x1"
- "p2:x2"
topic: "/myLastWill"
message: "@/path2my/will.yaml"