[Search] Add support for generalised CSAs in the sdsl, such that we can index text collections without artificially adding a sentinel character to our indices.

[rrahn]

Description

This involves also a correct implementation of the generalised SACA.
What can we use as a SACA?
What about sentinels?
Can we adapt the existing algorithms?

Acceptance Criteria

• after this spike we can plan and import/implement a generalised SACA

Tasks

• Look for possible algorithms to construct a generalised SA
• The design should also allow a sentinel-free implementation.