Update how nextLink value is retrieved

Currently the nextLink/after value is retrieved by removing the brackets and saving the contents. However, it is done by assuming that the brackets are in the first and last positions of the string. We need to update it to ensure that we do not delete any relevant information in case the brackets are not there.

Solutions:
1) Using `IndexOf` and `LastIndexOf` functions to check if the brackets exist and use their positions to delete them with regex (Similar to the way that it is done now)
2) Using only regex to only use the information found inside the brackets if they exist.

This task is made in reference to the following comment:
https://github.com/Azure/data-api-builder/pull/2893#discussion_r2413840792

Comienza revisando la discusión del pull request referenciado y localizando el código que recupera el valor nextLink/after. Confirma el manejo actual de los corchetes y, después, verifica que los valores entre corchetes se extraigan, mientras que los valores sin corchetes conserven toda la información relevante.

Escrito por el modelo de indexación a partir del texto del issue.