Enable persistence for specific collection(s) only

### [REQUIRED] Describe your environment

* Operating System version: Mac
* Browser version: Chrome 80.03
* Firebase SDK version: 7.12
* Firebase Product: database

### [REQUIRED] Describe the problem
I would like to request for a feature where user can enable persistence for collection they want.
I have a scenario where I would like to have a minimal cache size and persistence needed for only one collection since other collection data reads might clog space unnecessarily.
#### Steps to reproduce:
Enable persistence, set cache size and read data from multiple collections.

#### Relevant Code:
NA