Add classmethod for initializing Sinequa class

[anisbhsl]

Description

This PR adds a from_config class method in Sinequa class to initialize Sinequa instance with given configuration dictionary.

Major Changes

1. Added from_config class method to initialize Sinequa instance.

Minor Changes

1. Updated docs (README)
2. Update tests to accommodate new secondary constructor.
3. Added few more docstrings.

Example Usage:

from pynequa import Sinequa
config= {
     "access_token" : "",
     "base_url": "",
     "app_name": "",
     "query_name": ""
}

sinequa = Sinequa.from_config(config)

OR do it directly using:

from pynequa import Sinequa
config= {
     "access_token" : "",
     "base_url": "",
     "app_name": "",
     "query_name": ""
}

sinequa = pynequa.Sinequa(
     access_token: config["access_token"],
     base_url: config["base_url"],
     app_name: config["app_name"],
     query_name: config["query_name"],
)

[NISH1001]

@anisbhsl can you also add the primary construction mechanism to pynequa usage? Something like Sinequa(...)

[anisbhsl]

@anisbhsl can you also add the primary construction mechanism to pynequa usage? Something like Sinequa(...)

I've added example usage in both the README and the description of this PR.