Add support for DreamGen API.

API docs: https://dreamgen.com/docs/models/opus/v1
API keys: https://dreamgen.com/account/api-keys

I decided to base this on the text-completion API since it's more
flexible with SillyTavern's prompt formating capabilities.

This also means that custom context and instruct settings are required.

Will add documentation in a followup PR.

public/scripts/secrets.js

@@ -17,6 +17,7 @@ export const SECRET_KEYS = {
     MISTRALAI: 'api_key_mistralai',
     TOGETHERAI: 'api_key_togetherai',
     INFERMATICAI: 'api_key_infermaticai',
+    DREAMGEN: 'api_key_dreamgen',
     CUSTOM: 'api_key_custom',
     OOBA: 'api_key_ooba',
 };
@@ -39,6 +40,7 @@ const INPUT_MAP = {
     [SECRET_KEYS.TOGETHERAI]: '#api_key_togetherai',
     [SECRET_KEYS.OOBA]: '#api_key_ooba',
     [SECRET_KEYS.INFERMATICAI]: '#api_key_infermaticai',
+    [SECRET_KEYS.DREAMGEN]: '#api_key_dreamgen',
 };
 
 async function clearSecret() {