[FEATURE] Oracle schemas

**Is your feature request related to a problem? Please describe.** We use Oracle where I work and wanted something nice to look into the DB, dblab looks like a nice solution. However, I haven't been able to get it to work. As far as I understand, Oracle creates a separate schema for every user and users can allow other users to access their tables. The problem is we usually don't have access to the user who owns the schema, but we can (and need to) see their tables. I could not find a way to do this in dblab. **Describe the solution you'd like** Add a flag, that is going to let me specify a schema (I think it already works for Postgres?) **Describe alternatives you've considered** I tried using the option for Postgres, just in case. Did not work. I could workaround by calling a select on the whole table from another schema, but that is annoying. **Additional context** I think this issue is the same thing for Postgres: https://github.com/danvergara/dblab/issues/95