Streamline ChatOptions

* Surface more configuration APIs to ChatOptions
* Use abstraction in Observations directly instead of dedicated implementation
* Simplify metadata config in observations for defined models
* Improve merging of runtime and default options in OpenAI
* Fix missing option in Mistral AI

Relates to gh-1148

Signed-off-by: Thomas Vitale <ThomasVitale@users.noreply.github.com>

models/spring-ai-postgresml/src/main/java/org/springframework/ai/postgresml/PostgresMlEmbeddingOptions.java

@@ -17,6 +17,7 @@ package org.springframework.ai.postgresml;
 
 import java.util.Map;
 
+import com.fasterxml.jackson.annotation.JsonIgnore;
 import com.fasterxml.jackson.annotation.JsonInclude;
 import com.fasterxml.jackson.annotation.JsonInclude.Include;
 import com.fasterxml.jackson.annotation.JsonProperty;
@@ -132,11 +133,13 @@ public class PostgresMlEmbeddingOptions implements EmbeddingOptions {
 	}
 
 	@Override
+	@JsonIgnore
 	public String getModel() {
 		return null;
 	}
 
 	@Override
+	@JsonIgnore
 	public Integer getDimensions() {
 		return null;
 	}