Allow database metadata to be saved to a local file

Would really like it if this were possible; I might be able to contribute if required. I would like the database to be a dependency only during the first build against it on my dev machine; having the database as a hard dependency on the build is a showstopper to using this library for us. Some other type providers allow this via a local schema file argument to the type provider. This helps with CI builds where you may not have access to the database to get the schema from (I.e. I can get it from a local data file instead). It also ensures builds can be repeatable by keeping versions metadata alongside the code.

Type dB = sqlcommandprovider < query, connectionString, LocalSchemaFile = "dbSchema.cache" >
If the file does not exist then use the database and run the query to get the types to be generated else use the file.

Start by locating the SqlCommandProvider entry point and how query metadata is fetched and generated; the issue names no files or tests. Trace the proposed LocalSchemaFile flow, then verify that an existing schema file avoids database access while a missing file falls back to the database, producing repeatable builds.