[v1.6] support embedders setting

[CommanderStorm]

Description
Currently, the embedders cannot be added via the sdk, only via http.

Basic example

instead of

curl \       
  -X PATCH 'http://localhost:7700/indexes/movies/settings' \
  -H 'Content-Type: application/json' \
  --data-binary '{
    "embedders": {
      "default": {
        "source": "huggingFace",
        "model": "bge-base-en-v1.5",
        "documentTemplate": "A movie titled '{{doc.title}}' whose description starts with {{doc.body|truncatewords: 20}}"
      }
    }
  }'

Settings::new().with_embedders(HashSet::from("default", Embedder::HuggingFace{...}))

Other
If adding such features to the sdk BEFORE they are out of the experimental stage, I could implement this.
If not, that is fine too ^^

[CommanderStorm]

@curquiza
You added the enhancement label. Does this mean I can work on this, or do you think that experimental features should only be implemented once stable? ^^

[curquiza]

Sorry, you are right, I was not clear at all.
Yes, you can work on this 😊

I'm curious, do you use this feature + rust SDK, or is it only to make an opensource contribution? 😊

[CommanderStorm]

I'm curious, do you use this feature + rust SDK

Yes, but not yet in production (in my uni, not a company).
I have toyed with it in an experimental project and thought that adding this to the sdk might be a good excuse to learn how this should be configured.