Deny unknown keys in settings in JSON schema so user gets warnings but settings still parses (#30583)

Closes #ISSUE

Release Notes:

- Improved checking of Zed settings so that unrecognized keys show
warnings while editing them

crates/assistant_settings/src/assistant_settings.rs

@@ -41,6 +41,7 @@ pub enum NotifyWhenAgentWaiting {
 
 #[derive(Clone, Debug, Serialize, Deserialize, JsonSchema, PartialEq)]
 #[serde(tag = "name", rename_all = "snake_case")]
+#[schemars(deny_unknown_fields)]
 pub enum AssistantProviderContentV1 {
     #[serde(rename = "zed.dev")]
     ZedDotDev { default_model: Option<CloudModel> },
@@ -543,6 +544,7 @@ impl AssistantSettingsContent {
 
 #[derive(Clone, Serialize, Deserialize, JsonSchema, Debug)]
 #[serde(tag = "version")]
+#[schemars(deny_unknown_fields)]
 pub enum VersionedAssistantSettingsContent {
     #[serde(rename = "1")]
     V1(AssistantSettingsContentV1),
@@ -576,6 +578,7 @@ impl Default for VersionedAssistantSettingsContent {
 }
 
 #[derive(Clone, Serialize, Deserialize, JsonSchema, Debug, Default)]
+#[schemars(deny_unknown_fields)]
 pub struct AssistantSettingsContentV2 {
     /// Whether the Assistant is enabled.
     ///
@@ -734,6 +737,7 @@ pub struct ContextServerPresetContent {
 }
 
 #[derive(Clone, Serialize, Deserialize, JsonSchema, Debug)]
+#[schemars(deny_unknown_fields)]
 pub struct AssistantSettingsContentV1 {
     /// Whether the Assistant is enabled.
     ///
@@ -763,6 +767,7 @@ pub struct AssistantSettingsContentV1 {
 }
 
 #[derive(Clone, Serialize, Deserialize, JsonSchema, Debug)]
+#[schemars(deny_unknown_fields)]
 pub struct LegacyAssistantSettingsContent {
     /// Whether to show the assistant panel button in the status bar.
     ///