Missing finalizer protection for XBackend referenced by HTTPRoute

[chuangw6]

Currently, the XBackend finalizer only checks for targeting XAccessPolicies. It does not check if the backend is still in use by any HTTPRoute. This allows an XBackend to be deleted out-of-order, causing the associated HTTPRoute to point to a non-existent resource.

[chuangw6]

@HarshithaMS005 would you mind taking a look at this? Thanks!

[HarshithaMS005]

@chuangw6 Sure will check thank you.

[HarshithaMS005]

/assign