[Feature] Dynamically exclude tokens from RAG output

[mawandm]

Description
We want the ability to exclude tokens based on an exclusion list combined with RBAC.

Detail
When handling some kind of information, some tokens need to be excluded. Two scenarios where this is necessary include;

1. Handling sensitive PII information. In this scenario it may be permitted for one user to view the sensitive information such as a customer service representative while another user may not be permitted to view the same sensitive information. In order to achieve this, an exclusion list must be created and associated to the roles of the respective user.
2. Filtering offensive language. This scenario can be useful when we want to exclude some perceived offensive tokens for example when there age restrictions.

Acceptance Criteria
This is an exploratory task so this list may be changed.

1. Add an exclusion list data source. This can include;
   1. SQL database
   2. REST API
   3. File upload
2. An exclusion list can be associated to a role.
3. Exclusion rules are applied to user dynamically.