If no value, we should default to current selected host

[nicobytes]

Parent Issue => #28494

Screenshots

If the siteFolder field is not required, it defaults to system host.

If the siteFolder field is required, it defaults to current host

[dsilvam]

Failed IQA:

1. Marked siteFolder as required
2. Opened new content dialog. It correctly had pre-selected the current site.
3. Hit save

If fails with the following error

https://gist.github.com/dsilvam/dda940bc803b7b051ca10ee5b2eef116

[dsilvam]

Passed Internal QA:

• Defaulting to System Host when the siteFolder field is not required
• Defaulting to Current Host when the siteFolder field is required.

Being able to save/publish the content on both cases.

[josemejias11]

Approved: Tested on trunk_6d3ea16, Docker, macOS 14.5, FF v126.0.1