Webhosting

### Is your feature request related to a problem?

Today, a transaction for hosting is an object with a liste of files as attributes.
This approach doesn’t allow to add additional information

### Describe the solution you'd like

The proposal is to have an object with metadata and an attribut such as ‘files’ with the same content as today.

So we can have additional fields like name/description, author etc.., ability to add headers in the response,… eventually an attribut having the address on a transaction containing a certificate (if https managed by Phoenix/elixir and not Nginx. Etc..)
Can specify the type site, lib (can be shared by other website) etc

### Additional context

_No response_

No files, tests, or entry points are named. Start by locating the current hosting transaction representation and define the scope for separating metadata from files; done should include an agreed schema covering the proposed response headers and optional certificate reference.

Written by the indexing model from the issue text.