fix(core) support route migration

[StarlightIbuki]

This PR is to support blue/green migration from 2.8.x to 3.0.x.

This PR needs #9334 to cooperate.

Fix FT-3293

[chronolaw]

I think it should not be in 3.0 milestone, it belongs to 2.8.x

[ADD-SP]

I have test this PR locally for Traditional Mode.

1. Bootstrap Postgres using image kong:2.7.1-alpine
2. Start container kong:2.7.1-alpine
3. Insert a prefix route, insert a regex route.
4. Keep traffic on kong-2.7.1
5. Run kong migrations up using this PR.
6. Start Kong using this PR.
7. Keep traffic on this PR's Kong
8. Stop container kong:2.7.1-alpine.
9. Run kong migrations finish using this PR's Kong.
10. Run kong migrations up using image kong:3.0.0-alpine
11. Start container kong:3.0.0-alpine.
12. Keep traffic on kong-3.0.0.
13. Stop this PR's Kong.
14. Run kong migrations finish using image kong:3.0.0-alpine.
15. Restart container kong:3.0.0-alpine.

During the test, all traffic was 200.

[StarlightIbuki]

Maybe we should merge this and then cherry-pick to EE with squashed commit.