fix(general): tolerate ${HTTPS_PROXY} without a scheme

[andrew-rowson-lseg]

Description

urllib3.ProxyManager is quite opinionated about the value passed in as the proxy URL, in that it must at least have a scheme. Creating a ProxyManager with a schemeless URL throws an exception:

urllib3.exceptions.ProxySchemeUnknown: Proxy URL had no scheme, should start with http:// or https://

Checkov passes the value of os.environ['https_proxy'] directly into ProxyManager in platform_integration.py so if this value happens to not start with http:// or https://, then checkov crashes out.

I couldn't find anything authoritative on whether ${HTTPS_PROXY} should or shouldn't have a scheme. The best reference I could find was from the curl manual (https://curl.se/docs/manpage.html) which shows the "protocol" part as being optional.

HTTPS_PROXY [protocol://][:port]

Given that it then seems valid for ${HTTPS_PROXY} to contain a bare hostname (or host:port) pair, and it's certainly true in my environment, this patch checks to see if a scheme is present in the env var and then adds in a default if its absent.

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my feature, policy, or fix is effective and works
• New and existing tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules