Add Google PaLM support

Author: andreibondarev

README.md

@@ -30,8 +30,8 @@ require 'weaviate'
 client = Weaviate::Client.new(
     url: 'https://some-endpoint.weaviate.network',  # Replace with your endpoint
     api_key: '', # Weaviate API key
-    model_service: :openai, # Service that will be used to generate vectors. Possible values: :openai, :azure_openai, :cohere, :huggingface
-    model_service_api_key: 'xxxxxxx' # Either OpenAI, Azure OpenAI, Cohere or Hugging Face API key
+    model_service: :openai, # Service that will be used to generate vectors. Possible values: :openai, :azure_openai, :cohere, :huggingface, :google_palm
+    model_service_api_key: 'xxxxxxx' # Either OpenAI, Azure OpenAI, Cohere, Hugging Face or Google PaLM api key
 )
 ```
 

lib/weaviate/client.rb

@@ -14,7 +14,8 @@ class Client
       openai: "X-OpenAI-Api-Key",
       azure_openai: "X-Azure-Api-Key",
       cohere: "X-Cohere-Api-Key",
-      huggingface: "X-HuggingFace-Api-Key"
+      huggingface: "X-HuggingFace-Api-Key",
+      google_palm: "X-Palm-Api-Key"
     }
 
     def initialize(