Clear and concise description of the problem

Some 3rd party components have been known to interfere with bootstrap default z-indexes. So we might want to add an option to add a starting point for example BModal.

Suggested solution

option to createBootstrap, or add a css var that can be added to our calculations with
z-index: calc(${ourZindex} + var(--bv-zindex-hoist, 0))

Alternative

No response

Additional context

No response