Prototype: User dictionary settings API

[cvermand]

Description
A new setting named wordDictionary is being introduced as a prototype in meilisearch. We would like to create a prototype version of meilisearch-js implementing the required changes to be able to try out the new setting.

Following this specification, we need to add:

• A GET route that fetches the setting
• A PUT route that updates the setting
• A Delete route that resets the setting
• Add the new setting in the settings types
• Add tests

Basic example

client.index('x').getWordDictionnary()
client.index('x').updateWordDictionnary(['x'])
client.index('x').resetWordDictionary()

[Clémentine]

Closed by #1573