These commits do a few things:

46b1303e62ea7e01ba6a441cc55bbe4c166ef5ce corrects a few minor mistakes with the new site config which I introduced in #63654 - namely fixing examples entries and nullability in a few cases. Nothing controversial here, just bug fixes.

750b61e7dfa661338c9b40042087aed8e795f900 makes it so that the /.api/client-config endpoint returns "modelsAPIEnabled": true, if "modelConfiguration" is set in the site config. For context, "modelConfiguration" is a new site config field, which is not used anywhere before this PR, and has this description:

BETA FEATURE, only enable if you know what you are doing. If set, Cody will use the new model configuration system and ignore the old 'completions' site configuration entirely.

I will send a change to the client logic next so that it uses this modelsAPIEnabled field instead of the client-side feature flag dev.useServerDefinedModels.

Finally, f52fba342dd2e62a606b885802f7f6bc37f4f4ac and bde67d57c39f4566dc9287f8793cb5ffd25955b3 make a few site config changes that @chrsmith and I discussed to enable Self-hosted models support. Specifically, it makes it possible to specify the following configuration in the site config:

  // Setting this field means we are opting into the new Cody model configuration system which is in beta.
  "modelConfiguration": {
    // Disable use of Sourcegraph's servers for model discovery
    "sourcegraph": null,

    // Configure the OpenAI-compatible API endpoints that Cody should use to provide
    // mistral and bigcode (starcoder) models.
    "providerOverrides": [
      {
        "displayName": "Mistral",
        "id": "mistral",
        "serverSideConfig": {
          "type": "openaicompatible",
          "endpoint": "...",
          "accessToken": "...",
        },
      },
      {
        "displayName": "Bigcode",
        "id": "bigcode",
        "serverSideConfig": {
          "type": "openaicompatible",
          "endpoint": "...",
          "accessToken": "...",
        },
      },
    ],

    // Configure which exact mistral and starcoder models we want available
    "modelOverridesRecommendedSettings": [
      "bigcode::v1::starcoder2-7b",
      "mistral::v1::mixtral-8x7b-instruct"
    ],

    // Configure which models Cody will use by default
    "defaultModels": {
      "chat": "mistral::v1::mixtral-8x7b-instruct",
      "fastChat": "mistral::v1::mixtral-8x7b-instruct",
      "codeCompletion": "bigcode::v1::starcoder2-7b",
    }
  }

Currently this site config is not actually used, so configuring Sourcegraph like this should not be done today, but this will be in a future PR by me.

@chrsmith one divergence from what we discussed.. me and you had planned to support this:

        "modelOverrides": [
            {
                "bigcode::v1::starcoder2-7b"": {
                    "useRecommendSettings": true,
                },
                "mistral::v1::mixtral-8x22b-instruct": {
                    "useRecommendSettings": true,
                },
             }
        ],

However, being able to specify "useRecommendSettings": true, inside of a ModelOverride in the site configuration means that all other ModelOverride fields (the ones we are accepting as recommended settings) must be optional, which seems quite bad and opens up a number of misconfiguration possibilities.

Instead, I opted to introduce a new top-level field for model overrides with recommended settings, so the above becomes this instead:

    "modelOverridesRecommendedSettings": [
      "bigcode::v1::starcoder2-7b",
      "mistral::v1::mixtral-8x7b-instruct"
    ],

This has the added benefit of making it impossible to set both "useRecommendSettings": true, and other fields.

I will make it a site config error (prevents admins from saving configuration) to specify the same model in both modelOverrides and modelOverridesRecommendedSettings in a future PR.

Test plan

Doesn't affect users yet. Careful review.

Changelog

N/A