[Feature Request] Add interval option for Update DM

### Is your feature request related to a problem? Please describe.

Whenever the bot DMs me about an update I often think it's someone asking for help rather than a bot sending a DM (As I only have DMs open for close friends and servers I act as support in). As I can't actually update it during the time I first get them, it's fairly inconvenient to get this same thing every day until the day I can actually update it as it takes my attention away from what I'm doing. I do however need to know when an update is out, so disabling the `updatealerts` option is not a solution, as I otherwise wouldn't know an update is out for possibly months.

### What is your ideal solution to the problem?

Add an second option that allows you to specify an interval. I'd recommend hours or days. But at least something that allows us to specify how often we'll be reminded.

I did also see #983 where you mention valid points why not to add it. If you're still on par with that despite my own points, do prefer to add an option of when during the day the bot should DM. Currently I get the DMs at around 1pm. If I could instead choose something like 8pm that would also be acceptable.

### How would this feature be used?

Let's say the option is called `updatealerts.interval`, here's a few examples of what different values would do, assuming hours:
1. `updatealerts.interval=24` - Sends a every day (Current behaviour).
2. `updatealerts.interval=48` - Sends a DM every 2 days.
3. `updatealerts.interval=168` - Sends a DM every week.
4. `updatealerts.interval=0` - Sends a DM only once.

As for the relation to #983 you'd possibly just have an option `updatealerts.time` which would be a 4 digit number specifying the time. `2000` would DM you at 8pm and `730` would DM you at 7:30am. This way you wouldn't need to change the 24 hour interval but could still allow us to get the DM when we're easily available.

### Additional Info

I'm also very sensitive to notifications in general due to mental issues, mostly ones that aren't expected. If someone DMs me about needing help, that's fine. If my bot DM me about an update once, that's fine too. But once I get either spam (which I've disabled DMs from strangers for a reason) or if my bot starts DMing me on an interval when I need not to, it does stress me out heavily. So options like this really help me in the long run as it's basic accessibility settings at that point.

### Checklist

- [X] I have checked [the documentation](https://jmusicbot.com/) to make sure this feature doesn't already exist
- [X] I have searched for [similar feature requests](https://github.com/jagrosh/MusicBot/labels/enhancement)
- [X] I have confirmed that my requests is **not** on the [list of things that will not be added](https://jmusicbot.com/things-that-wont-be-added)
- [X] I am running the latest version of the bot: 

No implementation files or tests are named. Search the repository for the existing updatealerts setting and its update-DM handling, then read issue #983 before choosing between an interval or scheduled-time design. Done means the selected behavior is implemented with validated configuration semantics and documented for users.

Written by the indexing model from the issue text.