Update HTTP URL to HTTPS URL

[bencomp]

What this PR does / why we need it:
This updates (almost) all HTTP URLs found in the documentation and code to HTTPS. It increases privacy of readers and may even save some time if the HTTP address needs to redirect to the HTTPS address.

Which issue(s) this PR closes:

I found the HTTP URLs after looking at #9054, but this is unrelated.

Special notes for your reviewer:
I manually checked that the HTTPS URLs resolve. Some do redirect to updated URLs, but I only updated the URL if the content matched the expected content. There may be exceptions to this rule.

I couldn't access the Phoenix server, so I kept those URLs the same.

Suggestions on how to test this:
For now, you could scan the changes and perhaps sample a few URLs to see that resolve to what you would expect.
In the future, you could use an automatic link checker.

Does this PR introduce a user interface change? If mockups are available, please link/include them here:
It does change the template of the Guides, so changes may be recognised on many users.

Is there a release notes update needed for this change?:
N/A
Additional documentation:

[bencomp]

Merge conflicts caused by #9616 efforts have been resolved.

[bencomp]

Updated URLs in the "classic dev environment". Hoping for a positive review 🤞

[bencomp]

Fixed merge conflict caused by merging #9796.

[qqmyers]

Straight-forward http -> https cleanup.