SQL Chain CVE fix

[Avr-Arnold]

I made a SQL chain and it didn't get implemented for security concerns. One of the things I have been trying, is to make the authorization dependent on the developer by using data/cached results provided by the developer. Those results can now be queried by langchain's SQL chain. I got this idea from Apache Superset's SQL Lab where they call it results backend. I also hope this can be generic enough to allow SQL queries against pandas and the like. What do you think?