Addition of pill-like aperture?

I have made and been using the pill type aperture. ([here](https://github.com/ysBach/ysphotutilpy/blob/master/ysphotutilpy/aperture.py#L445). I named it `PillBox` as it is a combination of elliptical and rectangular("box") aperture, but I think `Pill` is a better name)

**Pill type aperture** is useful for **trailed objects** (non-sidereal observation like asteroids and comets).

A figure from Fraser et al 2016 (http://dx.doi.org/10.3847/0004-6256/151/6/158) with some annotations:
Their package is [TRIPPy](https://github.com/fraserw/trippy)

Thanks to elliptical aperture in photutils, I could make the rounded parts at the ends in elliptical shape. This has been used in some publications I was involved in (e.g., [Ishiguro, Bach et al. MNRAS (2022)](https://doi.org/10.1093/mnras/stab3198)). One difficulty is that, as I heavily followed the internal form of other apertures (such as `EllipticalAperture` class), when the internal API in `photutils` changes, some users and my class students complain my package raises `ImportError`s. Thus, I think it maybe beneficial if this `PillAperture` and related codes can be included into photutils.

If you think it is reasonable, I will try to make a PR (may take a few weeks though). How do you think?

Start with the linked implementation in ysphotutilpy/aperture.py around line 445, including the PillBox/PillAperture design, and compare it with the existing aperture classes referenced in the issue. Determine the API and scope for adding a pill-shaped aperture to photutils; done requires a maintainer-approved design and a complete PR plan.

Written by the indexing model from the issue text.