Add New Case | Case Details | Drug Related Charge | Add Estimated Sentence

### Background on the problem the feature will solve/improved user experience
As a Public Defender/Staff Member, I want to add estimated sentence length measured in months when adding a new drug related case. Currently, the estimated sentence dropdown shows a list of races when clicked.

### Describe the solution you'd like
The dropdown should be replaced with a text box that receives numerical input for the number of months of sentence estimated, with some kind of indication (maybe the hint in the text box) that the sentence length is measured in months.

### Tasks

- [ ] Replace the current dropdown with a text box that receives numerical input
- [ ] Add tests

### Acceptance Criteria
The user should be presented with a text box that receives numerical input for the estimated sentence length in months.