[Network] Doc deprecation message to router_route_v2 and refactoring

[anton-sidelnikov]

Summary of the Pull Request

Resource not presented in docportal, it means that it is deprecated.
But still works, so refactored and added test case with instance recreation.

PR Checklist

• Refers to: opentelekomcloud_networking_router_route_v2 does not handle disappeared routes well #2652
• Tests added/passed.
• Documentation updated.
• Schema updated.
• Release notes added.

Acceptance Steps Performed

=== RUN   TestAccNetworkingV2RouterRoute_basic
=== PAUSE TestAccNetworkingV2RouterRoute_basic
=== CONT  TestAccNetworkingV2RouterRoute_basic
--- PASS: TestAccNetworkingV2RouterRoute_basic (233.55s)
PASS

=== RUN   TestAccNetworkingV2RouterRoute_ecs
=== PAUSE TestAccNetworkingV2RouterRoute_ecs
=== CONT  TestAccNetworkingV2RouterRoute_ecs
--- PASS: TestAccNetworkingV2RouterRoute_ecs (340.75s)
PASS

Debugger finished with the exit code 0

[otc-zuul]

Build succeeded.
https://zuul.otc-service.com/t/eco/buildset/80da7d729c1a482ca26cccd6b0307aa9

✔️ build-otc-releasenotes SUCCESS in 3m 54s
✔️ noop SUCCESS in 0s
✔️ otc-golangci-lint SUCCESS in 3m 14s
✔️ golang-make-test SUCCESS in 3m 48s
✔️ golang-make-vet SUCCESS in 2m 36s
✔️ tflint SUCCESS in 1m 45s
✔️ goreleaser-build SUCCESS in 7m 49s