Merge #3505

3505: Csv delimiter r=irevoire a=irevoire

Fixes https://github.com/meilisearch/meilisearch/issues/3442
Closes https://github.com/meilisearch/meilisearch/pull/2803
Specified in https://github.com/meilisearch/specifications/pull/221

This PR is a reimplementation of https://github.com/meilisearch/meilisearch/pull/2803, on the new engine. Thanks for your idea and initial PR `@MixusMinimax;` sorry I couldn’t update/merge your PR. Way too many changes happened on the engine in the meantime.

**Attention to reviewer**; I had to update deserr to implement the support of deserializing `char`s

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It introduces four new error messages;
- Invalid value in parameter csvDelimiter: expected a string of one character, but found an empty string
- Invalid value in parameter csvDelimiter: expected a string of one character, but found the following string of 5 characters: doggo
- csv delimiter must be an ascii character. Found: 🍰 
- The Content-Type application/json does not support the use of a csv delimiter. The csv delimiter can only be used with the Content-Type text/csv.

And one error code;
- `invalid_index_csv_delimiter`

The `invalid_content_type` error code is now also used when we encounter the `csvDelimiter` query parameter with a non-csv content type.

Co-authored-by: Tamo <tamo@meilisearch.com>

milli/Cargo.toml

@@ -19,7 +19,7 @@ byteorder = "1.4.3"
 charabia = { version = "0.7.0", default-features = false }
 concat-arrays = "0.1.2"
 crossbeam-channel = "0.5.6"
-deserr = "0.4.1"
+deserr = "0.5.0"
 either = "1.8.0"
 flatten-serde-json = { path = "../flatten-serde-json" }
 fst = "0.4.7"