I want to be able to use "ASL Y" in VRChat when using Index Emulation.

First, awesome, amazing work with the index emulation! However, I need to be able to customise the gestures or revert to having the default set available which would otherwise be normally available to quest users.

## Description

For sign language, particularly with the adaption of ASL called VR-ASL, we need to use the "Y" handshake, as follows: https://www.handspeak.com/word/2484/

Normally with Quest Controllers, we can do this. It'll either be the Y (as show in the link above), or it'll be the "horns" gesture, but either way, we get that little finger up and we can use conventions in VR-ASL to describe the signs that use that finger.

By default, using the same input on the Quest that I would normally use to produce this gesture, in ALVR, it produces the "rude finger" gesture (ie, the middle finger). Which sure is amusing! However, that's fine as long as there's another way of getting that Y handshape, and right now, I don't think there's a configurable way to do so.

I considered trying the regular quest controller settings (ie, not using index emulation), however, the additional handshapes in index emulation are very nice and it also means that when I use hand tracking, to approximate the hand poses using index emulation, it works pretty nicely.

So, I am wondering how I might customise the index emulation so that when I use the quest controllers, I can still express signs using that "Y" handshape.

## General Troubleshooting
- [x] I carefully followed the instructions in the [README](https://github.com/alvr-org/ALVR/blob/master/README.md) and successfully completed the setup wizard
- [x] I read the ALVR Wikis [here](https://github.com/polygraphene/ALVR/wiki) and [here](https://github.com/alvr-org/ALVR/wiki)

## Environment

Quest 2.
VRChat.
Latest Nightly for ALVR as was available on April 23 2023, which is ALVR v20.0.0-dev11+nightly.2023.04.22

### Hardware
N/A, other than that I'm using Quest 2 in PCVR mode.

### Installation
ALVR v20.0.0-dev11+nightly.2023.04.22

**SteamVR Version**: Recently updated.

**Install Type**:

I think it was the "portable" version given that I used the nightly .zip

**OS Name and Version** (`winver` on Windows or `grep PRETTY_NAME /etc/os-release` on most Linux distributions):
Windows, but I doubt it's relevant for this one.

### Feature Requests
> The quickest way to get a new feature is to file a pull request; these will be considered, but may be closed if they're something we're not actively planning to work on.

Ah, so yeah, this is a feature request. I might look at making a pull request at some point in the future (Unlikely to be this or next month). Some guidance in knowing where to look could be appreciated and if it looks simple enough, I might try making a hard-wired change myself. I have not yet looked at the code, although I do have some familiarity with Rust.