feat: Add prompt to proceed if http proxy is set and https proxy unset

[screspod]

What this PR does / why we need it:

Installation fails if http_proxy is configured but https_proxy is not set.
This PR adds the following confirmation prompt before proceeding with an installation:

Typically if `http_proxy` is set, `https_proxy` should be set too. Installation failures are likely otherwise. Do you want to continue anyway? (y/N)

Which issue(s) this PR fixes:

https://app.shortcut.com/replicated/story/121629/prompt-if-http-proxy-is-set-but-not-https-proxy

Does this PR require a test?

Unit tests have been added to verify:

• When a vendor confirms they want to continue the installation with http_proxy set and https_proxy unset.
• When a vendor confirms they DO NOT want to continue the installation with http_proxy set and https_proxy unset.

Does this PR require a release note?

Added confirmation prompt to prevent installation failures when `http_proxy` is set but `https_proxy` is missing.

Does this PR require documentation?

NONE

[screspod]

Closing this. Opened from a fork which led to a lack of access to credentials necessary for the Github actions to run successfully.