Don't assume the host URI scheme is https

[pepicrft]

WHY are these changes introduced?

We'll allow loading apps from localhost through http in the upcoming CLI release. To make it work, we need to adjust the logic in this package to not assume that the URI scheme is https.

WHAT is this pull request doing?

I'm removing the https assumption and allowing the consumer of the package to configure the URI scheme through the new context attribute, HOST_SCHEME. To make the change backward-compatible, I'm defaulting to https when no value is provided.

Type of change

• Patch: Bug (non-breaking change which fixes an issue)
• Minor: New feature (non-breaking change which adds functionality)
• Major: Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist

• I have added a changelog entry, prefixed by the type of change noted above
• I have added/updated tests for this change
• I have documented new APIs/updated the documentation for modified APIs (for public APIs)

[gonzaloriestra]

👌

[paulomarg]

LGTM code-wise, just a comment around testing!