Validation when specifying custom host

[itsyme]

Please confirm that you have searched existing issues in the repo

Yes, I have searched the existing issues

Any related issues?

#2382

What is the area that this feature belongs to?

No response

Is your feature request related to a problem? Please describe.

Specifying a custom host in #2395 could cause some unhandled errors to be exposed to the user after the building of pages when the specified host is not valid. This could lead to

1. Users being confused by the unhandled error
2. Users having to wait till the pages are finished building to realise there is an error

which could create a not so good UX.

Describe the solution you'd like

Validate the host before the building of pages. Should discuss what should be validated and what should not as well.

Describe alternatives you've considered

No response

Additional context

No response

[itsyme]

@LamJiuFong would you like to tackle this issue since you were working on the specifying custom host feature?