Add gazetteer configuration and dependency

This commit introduces the `VOCAB_DIR` configuration option, which
specifies the directory for gazetteer files. It also adds the `strsim`
crate, which is used for calculating string similarity and is essential
for the gazetteer's functionality.

The gazetteer module has been significantly expanded to include the
`Gazetteer` struct, its loading mechanism from `.txt` files, and an
annotation function. This functionality allows for pre-LLM correction of
proper names and technical vocabulary by identifying potential
misspellings based on phonetic similarity and edit distance.

server/Cargo.lock

@@ -345,6 +345,7 @@ dependencies = [
  "rpassword",
  "serde",
  "serde_json",
+ "strsim",
  "tempfile",
  "time",
  "tokio",
@@ -1642,6 +1643,12 @@ version = "1.2.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "6ce2be8dc25455e1f91df71bfa12ad37d7af1092ae736f3a6cd0e37bc7810596"
 
+[[package]]
+name = "strsim"
+version = "0.11.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7da8b5736845d9f2fcb837ea5d9e2628564b3b043a70948a3f0b778838c5fb4f"
+
 [[package]]
 name = "subtle"
 version = "2.6.1"