fix: update key validation to work with OpenAI's new project keys (#98)

fixes #97

OpenAI has introduced project keys as the new default over user keys (See: https://help.openai.com/en/articles/9186755-managing-your-work-in-the-api-platform-with-projects). This was a breaking change for those with old 'user keys', causing the validation to fail. 

Change itself was simple, consisting of 1 line at /src/utils/apikey.ts

src/utils/apikey.ts

@@ -1,3 +1,3 @@
 export function isValidAPIKey(apiKey: string | null) {
-  return apiKey?.length == 51 && apiKey?.startsWith("sk-");
+  return (apiKey?.length === 51 && apiKey.startsWith("sk-")) || (apiKey?.length === 56 && apiKey.startsWith("sk-proj-"));
 }