Add dynamic config support to test_connectivity example

[amircybersec]

This PR adds support for ssconfig:// dynamic config loading and parsing to test_connectivity that is compliant with existing formats as well as SIP008. This can be later refactored into config package

Some references:

• https://www.v2fly.org/en_US/v5/config/service/subscription.html#subscription-container
• https://www.reddit.com/r/outlinevpn/wiki/index/dynamic_access_keys/
• https://liolok.com/v2ray-subscription-parse/
• https://github.com/Shadowsocks-NET/OpenOnlineConfig/blob/master/docs/0002-open-online-config-v1-shadowsocks.md

Supports using pad.riseup.net, github gists, google spreadsheet, etc