Decouple host property in VirtualServerRoute

[nginx-seanmoloney]

Problem: The VSR host must exactly match the VS host, forcing 1:1 coupling and preventing reuse across hosts.​

Example:

• Company runs 20 regional e-commerce sites: us.shop.com, uk.shop.com, de.shop.com, etc.
• All sites share 5 common paths: /cart, /checkout, /account, /search, /api
• Today, they must create 20 VS × 5 VSRs for each site = 100 duplicate VSR objects, each identical except for the host field

Result: Updating any routing logic requires editing 20 separate VSRs; configuration drift and high maintenance

Acceptance Criteria:

• Make the host property optional in VirtualServerRoute
• Ensure backwards compatibility is maintained and that existing deployments are not impacted
• Update documentation and add new examples to the repository

[artem-zinnatullin]

Absolute +1, this requirement significantly and unnecessarily complicates the configuration and templating. In many cases the downstream microservice that exposes a VirtualServerRoute shouldn't even know the external host name that VirtualServer is using to match the requests.

VirtualServerRoute should be embeddedable into ~ any VirtualServer without knowing implementation details of given VirtualServer and it should be embeddable into multiple VirtualServers with different host names.

My understanding of the design is that VirtualServer roughly maps to Nginx core server https://nginx.org/en/docs/http/ngx_http_core_module.html#server and VirtualServerRoute roughly maps to location https://nginx.org/en/docs/http/ngx_http_core_module.html#location, well, core Nginx doesn't enforce any host name matching for location blocks obviously, why should VirtualServerRoute care about it?