Add support for config file

[tangledbytes]

Explain the changes

This PR adds support for config file. The following things are supported right now:

1. All the persistent/global flags can be specified in the config file instead of passing as a flag.
2. resources field is supported in the config file which allows overriding the default resources allocated to NooBaa components. This field can be used in conjunction with pre-existing flags like --dev and --mini in which case the values from the config file will override the values of the flag.

The config file can be placed at /etc/noobaa/noobaa.cfg.yaml, ~/.noobaa/noobaa.cfg.yaml or at ./noobaa.cfg.yaml.

Example config file

# This will override the namespace of installation
namespace: noobaa-test

# This will override the operator image
operator-image: noobaa/noobaa-operator:5.15.0

# This will override the show-secrets which defaults to false
show-secrets: true

# This is equivalent to using `--dev`
dev: true

# This is a special field which is unavailable in the CLI via flags
resources:
  core:
    memoryMB: 512
  db:
    cpuMilli: 500
    memoryMB: 1024
  endpoints:
    cpuMilli: 500
    memoryMB: 1024
    minCount: 1
    maxCount: 3 

• Doc added/updated
• Tests added

[liranmauda]

LGTM, just one comment/question

[liranmauda]

I couldn't figure out when this can happen.

[tangledbytes]

I think this can happen when say the config file is not valid (valid as in not adhering to yaml spec) yaml. In such cases we would want just log that there was some issue in reading the file.