Add ability to configure db folder location

[BryceRussell]

Currently, when using Astro DB inside a theme, the default folder location is inside the theme root like package/db. ATP could offer authors a way to customize the location of the folder instead of hardcoding it. This should be a fairly easy change, great for a first time contributor!

Relevant Links:

• https://github.com/astrolicious/astro-theme-provider/blob/main/package/src/index.ts#L107-L108
• https://github.com/astrolicious/astro-theme-provider/blob/main/package/src/internal/types.ts#L27