How to fill in missing date strings in SQL Select statement?

Question

I have a table that looks like this:

     ds     |  num_teams
--------------------------
 2020-01-08 |     13
 2020-01-05 |      9
 2020-01-02 |     11
 2019-12-31 |      8

But I need to fill in the missing date strings in a way that's consistent with increases / decreases, resulting in something like this:

     ds     |  num_teams
--------------------------
 2020-01-08 |     13
 2020-01-07 |      9
 2020-01-06 |      9
 2020-01-05 |      9
 2020-01-04 |     11
 2020-01-03 |     11
 2020-01-02 |     11
 2020-01-01 |      8
 2019-12-31 |      8

This is also a read-only database so it has to be done in a SQL SELECT statement, so I'm thinking it might be possible using OVER() somehow?