feat(all): Task store

implements:
https://github.com/meilisearch/specifications/blob/develop/text/0060-refashion-updates-apis.md

linked PR:

- #1889
- #1891
- #1892
- #1902
- #1906
- #1911
- #1914
- #1915
- #1916
- #1918
- #1924
- #1925
- #1926
- #1930
- #1936
- #1937
- #1942
- #1944
- #1945
- #1946
- #1947
- #1950
- #1951
- #1957
- #1959
- #1960
- #1961
- #1962
- #1964

- https://github.com/meilisearch/milli/pull/414
- https://github.com/meilisearch/milli/pull/409
- https://github.com/meilisearch/milli/pull/406
- https://github.com/meilisearch/milli/pull/418

- close #1687
- close #1786
- close #1940
- close #1948
- close #1949
- close #1932
- close #1956

meilisearch-http/src/option.rs

@@ -45,8 +45,8 @@ pub struct Opt {
     pub max_index_size: Byte,
 
     /// The maximum size, in bytes, of the update lmdb database directory
-    #[structopt(long, env = "MEILI_MAX_UDB_SIZE", default_value = "100 GiB")]
-    pub max_udb_size: Byte,
+    #[structopt(long, env = "MEILI_MAX_TASK_DB_SIZE", default_value = "100 GiB")]
+    pub max_task_db_size: Byte,
 
     /// The maximum size, in bytes, of accepted JSON payloads
     #[structopt(long, env = "MEILI_HTTP_PAYLOAD_SIZE_LIMIT", default_value = "100 MB")]