Investigate minSdk requirement

### Is there an existing issue for this?

- [X] I have searched the existing issues

### What happened?

Android Lollipop (API 21) appears to be used by 2% of devices globally according to https://apilevels.com, so I think we should be save to bump the minSdk requirement to a higher version

Currently, [Jetpack Compose requires minSdk = 21+](https://developer.android.com/jetpack/compose/setup#create-new), which is what the app currently uses:

https://github.com/EdricChan03/studybuddy-android/blob/011cb7d041628b6a66ec20e9fe078d0bd8cbf854/app/build.gradle.kts#L56

However, there's probably no real benefit in supporting such a low percentile 🤷

### Expected behaviour

minSdk should be a higher version to allow for newer Android features to be used without having to backport changes (e.g. removing explicit Marshmallow checks for runtime permissions, weird behaviours on older versions), etc

### Reproduction steps

N.A.

### Application variant

Release, Debug, Nightly

### Application version

_No response_

### Application version code

_No response_

### Relevant log output

_No response_

### Possible solution

We can:

- bump minSdk to a higher version, or
- backport any relevant libraries that requires a higher minSdk to 21 if necessary (probably not the ideal solution)

### Additional context

Trying to incorporate [Telephoto (image zooming composable)](https://saket.github.io/telephoto/) into the app, which requires minSdk = 23 as of 0.4.0