add optional ShopifyAPI::Context::httparty_params

[senid231]

Description

Fixes #1375

Adds the ability to configure a proxy server for all ShopifyAPI HTTP requests

ShopifyAPI::Context.setup(
  # other params...
  httparty_params: {
    timeout: 60, # Set the open/read/write timeout for HTTP requests
    open_timeout: 60, # Set the open timeout for HTTP requests
    read_timeout: 60, # Set the read timeout for HTTP requests
    write_timeout: 60, # Set the write timeout for HTTP requests
    debug_output: false, # Set to true to enable debug output for HTTP requests
    http_proxyaddr: "http://proxy.example.com:8080", # Set the HTTP proxy address
    http_proxyport: 8080, # Set the HTTP proxy port
    http_proxyuser: "username", # Set the HTTP proxy username
    http_proxypass: "password", # Set the HTTP proxy password
  }
)

How has this been tested?

proxy server configuration can't be tested via WebMock because it ignores proxy settings

Checklist:

• My commit message follows the pattern described in here
• I have performed a self-review of my own code.
• I have added tests that prove my fix is effective or that my feature works.
• I have updated the project documentation.
• I have added a changelog line.