Merge #4456

4456: Add Ollama as an embeddings provider r=dureuill a=jakobklemm

# Pull Request

## Related issue
[Related Discord Thread](https://discord.com/channels/1006923006964154428/1211977150316683305)

## What does this PR do?
- Adds Ollama as a provider of Embeddings besides HuggingFace and OpenAI under the name `ollama`
- Adds the environment variable `MEILI_OLLAMA_URL` to set the embeddings URL of an Ollama instance with a default value of `http://localhost:11434/api/embeddings` if no variable is set
- Changes some of the structs and functions in `openai.rs` to be public so that they can be shared.
- Added more error variants for Ollama specific errors
- It uses the model `nomic-embed-text` as default, but any string value is allowed, however it won't automatically check if the model actually exists or is an embedding model

Tested against Ollama version `v0.1.27` and the `nomic-embed-text` model.

## PR checklist
Please check if your PR fulfills the following requirements:
- [x] Does this PR fix an existing issue, or have you listed the changes applied in the PR description (and why they are needed)?
- [x] Have you read the contributing guidelines?
- [x] Have you made sure that the title is accurate and descriptive of the changes?

Co-authored-by: Jakob Klemm <jakob@jeykey.net>
Co-authored-by: Louis Dureuil <louis.dureuil@gmail.com>

milli/src/vector/openai.rs

@@ -419,12 +419,12 @@ impl Embedder {
 
 // retrying in case of failure
 
-struct Retry {
-    error: EmbedError,
+pub struct Retry {
+    pub error: EmbedError,
     strategy: RetryStrategy,
 }
 
-enum RetryStrategy {
+pub enum RetryStrategy {
     GiveUp,
     Retry,
     RetryTokenized,
@@ -432,23 +432,23 @@ enum RetryStrategy {
 }
 
 impl Retry {
-    fn give_up(error: EmbedError) -> Self {
+    pub fn give_up(error: EmbedError) -> Self {
         Self { error, strategy: RetryStrategy::GiveUp }
     }
 
-    fn retry_later(error: EmbedError) -> Self {
+    pub fn retry_later(error: EmbedError) -> Self {
         Self { error, strategy: RetryStrategy::Retry }
     }
 
-    fn retry_tokenized(error: EmbedError) -> Self {
+    pub fn retry_tokenized(error: EmbedError) -> Self {
         Self { error, strategy: RetryStrategy::RetryTokenized }
     }
 
-    fn rate_limited(error: EmbedError) -> Self {
+    pub fn rate_limited(error: EmbedError) -> Self {
         Self { error, strategy: RetryStrategy::RetryAfterRateLimit }
     }
 
-    fn into_duration(self, attempt: u32) -> Result<tokio::time::Duration, EmbedError> {
+    pub fn into_duration(self, attempt: u32) -> Result<tokio::time::Duration, EmbedError> {
         match self.strategy {
             RetryStrategy::GiveUp => Err(self.error),
             RetryStrategy::Retry => Ok(tokio::time::Duration::from_millis((10u64).pow(attempt))),
@@ -459,11 +459,11 @@ impl Retry {
         }
     }
 
-    fn must_tokenize(&self) -> bool {
+    pub fn must_tokenize(&self) -> bool {
         matches!(self.strategy, RetryStrategy::RetryTokenized)
     }
 
-    fn into_error(self) -> EmbedError {
+    pub fn into_error(self) -> EmbedError {
         self.error
     }
 }