[AGENT] Agents/ assistants

Feedback from open-source tells us that providing users with the ability to create agents is important. Technically speaking, agents are auto-regressive models, which have the ability to execute code/ functions depending on the output of these models. We can incorporate this functionality easily using `postprocess` and `preprocess`. In addition, by adding models which can search for data, we can add additional inputs to our models which reference the data in the `db`. - [x] #1551 - [x] #1552 - [x] #1553 - [x] #1554 - [x] #1555