Chore: add function to use RC20 Permit extension

This issue is to readd a previously removed function `_acquireMembershipWithPermit`, see [ad0dc9a81d892864ac2576d74e628ce93da592ef](https://github.com/waku-org/waku-rlnv2-contract/commit/ad0dc9a81d892864ac2576d74e628ce93da592ef)

This will allow the token approval step and registration step to be done together.