feat: support capability to retrieve documents based on the File Category user selection

[lschim]

To support the feature in the front-end to retrieve documents based on their File categories, the following tasks are required on the back-end side :

• Add a field contentTypeCategory in ES documents (computed from contentType)
• Compute contentTypeCategory value in the index stage
• Create a new Categorize stage to fill contentTypeCategory of the existing documents in ES (the one indexed before the addition of the feature)