[v1.4] Support user-dictionary loading

[Clémentine]

Following this central issue

• Add a new setting: dictionary with get, update, and reset methods associated.
  Here are the JS equivalents in meilisearch-js you should create for this repository:

client.index('indexName').getDictionary(); // calls GET /indexes/:uid/settings/dictionary
client.index('indexName').updateDictionary(['|', '/', '&sep']);  // calls PUT /indexes/:uid/settings/dictionary
client.index('indexName').resetDictionary(); // calls DELETE /indexes/:uid/settings/dictionary

• The methods associated with the /settings API route (to get, reset and update the settings globally) must be able to receive in the payload the new configuration dictionary.
• ⚠️ Add integration tests ⚠️
• Update the .code-samples.meilisearch.yaml
  • Add get_dictionary_1 key and “translate” the following curl example by using the newly added methods: https://github.com/meilisearch/documentation/blob/2060089a5c10bcd0beb28633062f90cf0b279f7f/.code-samples.meilisearch.yaml#L1133
  • Add update_dictionary_1 key and “translate” the following curl example by using the newly added methods: https://github.com/meilisearch/documentation/blob/2060089a5c10bcd0beb28633062f90cf0b279f7f/.code-samples.meilisearch.yaml#L1136
  • Add reset_dictionary_1 key and “translate” the following curl example by using the newly added methods: https://github.com/meilisearch/documentation/blob/2060089a5c10bcd0beb28633062f90cf0b279f7f/.code-samples.meilisearch.yaml#L1144