Add preflight handling for custom web image

[jayjb]

Proposed changes

We have added support recently for CORS, except in some cases there is a CORS preflight request. You can read more about it here. We need to handle it appropriately to continue.

Types of changes

What types of changes does your code introduce to this repository?
Put an x in the boxes that apply

• New feature (non-breaking change which adds functionality)

Checklist

Put an x in the boxes that apply. You can also fill these out after creating the PR. If you're unsure about any of them, don't hesitate to ask. We're here to help! This is simply a reminder of what we are going to look for before merging your code.

• Lint and unit tests pass locally with my changes (if applicable)
• I have run pre-commit (pre-commit in the repo)
• I have added tests that prove my fix is effective or that my feature works
• Linked to the relevant github issue or github discussion (Enable wildcard CORS support #329)