feat(sdk): allow for multi config

[ZXYmania]

allow each client to have a seperate config

• Example usage

from staxapp.config import Config
from staxapp.openapi import StaxClient

Config.access_key = "0ba825b2-ad6a-4b51-9189-26c20ecb57e3"
Config.secret_key = "first default config"
Config.hostname = "api.core.dev.juma.cloud"

# Use default creds to hit the Api
api_response = Api.get(f"/20190206/accounts")

# Read all accounts within your Stax Organisation
accounts = StaxClient("accounts")
response = accounts.ReadAccounts()

# Able to create instances of configs with the infomation set
second_config = Config(access_key = "aea77423-7cf0-48c4-9397-43fca29683e2", secret_key = "first custom config", hostname = "api.core.test.juma.cloud")
second_accounts = StaxClient("accounts", config=second_config)
s_response = second_accounts.ReadAccounts()

# Hit the Api with a custom config
second_config.init()
api_response_2 = Api.get(f"/20190206/accounts", None, second_config)

# Can have multiple default clients each client will be locked to what was default at time of creation
Config.access_key = "22225b2-ad6a-4b51-9189-26c20ecb57e3"
Config.secret_key = "second default config"
Config.hostname = "api.core.dev.juma.cloud"

workloads = StaxClient("workloads")
work_response = workloads.ReadWorkloads()

# Can create a config and the update the information
third_config = Config()
third_config.access_key = "0ba36500-abb3-48b2-8654-6c8fd0be0f29"
third_config.secret_key = "2nd custom config"

#The clients config will not be affected by changes to the original config
third_accounts = StaxClient("accounts", config=third_config)
third_config.access_key = None
t_response = third_accounts.ReadAccounts()

# Empty configs will be empty until assigned
fourth_config = Config()
fourth_accounts = StaxClient("accounts", config=fourth_config)
try:
    fourth_accounts.ReadAccounts()
except InvalidCredentialsException:
    print("You must specify creds for every new config")

• What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)
  Feature: allow for each client to have their own config and auth.

• What is the current behavior? (You can also link to an open issue here)
  Currently all auth and config is globally applied

• Does this PR introduce a breaking change? (What changes might users need to make in their application due to this PR?)
  Backwards compatibility has been maintained by retaining a global config that can be used in addition to config instances

[Anton0]

This seems like a good approach to me, I think it'd be nice to have some notes on this in the README.md since auth is normally the first task someone needs to solve to get the SDK up and running, or perhaps an example that shows multiple clients like your PR description.

[codecov]

Codecov Report

Merging #86 (9043ab6) into master (cfdd181) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master       #86   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            8         8           
  Lines          436       474   +38     
=========================================
+ Hits           436       474   +38     

Impacted Files	Coverage Δ
staxapp/api.py	100.00% <100.00%> (ø)
staxapp/auth.py	100.00% <100.00%> (ø)
staxapp/config.py	100.00% <100.00%> (ø)
staxapp/contract.py	100.00% <100.00%> (ø)
staxapp/openapi.py	100.00% <100.00%> (ø)