Refactoring of mapping between the upstream tool/resource/prompt name to downstream name #6450

At the moment:

1. We do expect that the downstream name is something like this "backend_name"-"upstream_tool_name".
2. We need this format because we use "backend_name" to find the details about the connection.
3. With the alias approach per backend we have an additional level of mapping ""backend_name"-"upstream_tool_name"-> "actual upstream name"

This is not great and very confusing. We are going to change to:

VirtualHost passed from the control plane structure needs to change from :

pub struct VirtualHost {
    pub backends: HashMap<String, BackendMCPGateway>,
}

To

pub struct VirtualHost {
    pub backends: HashMap<backend-name BackendMCPGateway>,
    pub tools: HashMap <downstream_name, (upstream_name, backend-name)>
}

This should be applied to:
tools, resources, resource_templates, prompts