Support for External Database Storage (PostgreSQL & MongoDB)

[iyashjayesh]

Description:
Currently, MoniGo is limited to local disk (tstorage) and in-memory backends. I propose adding support for external databases, specifically PostgreSQL and MongoDB, to allow for more robust data persistence.

Proposed Solution:

• Implement the Storage interface for Postgres and MongoDB.
• Extend the Builder API with methods like .WithPostgresStorage(url) and .WithMongoStorage(url, dbName).
• Keep local disk storage as the default fallback.

Benefits:

• Scalability: Supports multi-instance deployments pushing to a single database.
• Persistence: Allows for long-term metric retention beyond local storage limits.
• Flexibility: Users can choose between relational (Postgres) or document-based (Mongo) storage depending on their existing infrastructure.