Add project as datasource

[maveonair]

This pull requests adds the project datasource.

Example

data "incus_project" "default" {
  name = "default"
}

output "project_config" {
  value = data.incus_project.default.config
}

resource "incus_instance" "d1" {
  project = data.incus_project.default.name
  image    = "images:debian/12"
  name     = "d1"
}

What's been done

• Added project datasource
• Added docs for project datasource
• Improved profile documentation