feat(core) explict flag for regex route.path

[StarlightIbuki]

Another solution for #9022.

fix CT-344

We need to remember to add migration, and also "back migration" for EE.

PLEASE MERGE AFTER: #9024

[bungle]

NOTE: this will break all existing:

1. scripts that call admin apis and want regexes.
2. yaml (and other config files) that are used to configure dbless, or import data into control plane, traditional node, or imported by deck.
3. kong ingress controller might also be affected

In that sense I think this is a too big of a change that comes too close to 3.0.0 release. That said, major version is the version to do these kind of changes. It can be a can of worms. @dndx could you comment on this?

[bungle]

It is wrong to use ~* prefix and do case-sensitive matching. The ~ should be case-sensitive match. See: https://github.com/Kong/kong/blob/master/kong/router.lua#L960

We only add ajo and not i modifier.

premature approval.