feat: improve support for replied-to messages

[KnorpelSenf]

Context shortcuts do not take take reply_to_message into account.

Replies are a bit of a gap in what grammY supports. This should be fixed. Here are some examples of what we'd like to do:

• Which entities does the message that is being replied to have?
• Does the message that is being replied to have a /start command?
• Is the message that is being replied to an image?
• Does the message that is being replied to have a caption that matches a regular expression?

Let's discuss a few ideas how to tackle this.

1. Take this pull request and apply it to everything else. This would mean that we have to introduce a lot of options everywhere.
2. Provide a namespace ctx.replyTo which lets us test for all sorts of things, such as ctx.replyTo.message for the message object, ctx.replyTo.hasCommand("start") to check for /start commands, ctx.replyTo.entities to cover this PQ here, and so on.
3. Provide a grammY plugin that does all of these things somehow.
4. Maybe yet another solution?

Originally posted by @KnorpelSenf in https://github.com/grammyjs/grammY/issues/413#issuecomment-1565913241

[KnorpelSenf]

I'd like to go with option 3 after grammY 2.0 is released.

[KnorpelSenf]

I added this to #110. Closing.