Update conda build numbers?

## 🚀 Feature
Would it be possible to add and update build numbers inside of `SRC_DIR/conda/dgl/meta.yaml`?

## Motivation

Hello DGL developers,

It looks like my team at Katana Graph is the main downloader of your [conda package](https://anaconda.org/dglteam/dgl/files). We very much like the features in your package and develop new features for it in our work. We've run into an issue today that the expected checksum for version 0.8.2 does not match the checksum our package installer was expecting. We believe what happened is the following.

- We downloaded and stored the checksum of a package at [this url](https://anaconda.org/dglteam/dgl/0.8.2/download/linux-64/dgl-0.8.2-py38_0.tar.bz2) 8 days ago.
- A new package of the same version replaced the package at the same url with a different checksum 7 hours ago.
- Our package installation software tried to use the new package, found that the checksums differed, and threw an error.

## Alternatives

As we would like our automations not to break, we would like to find a solution such that a package at a fixed url can never changed its checksum value.

## Pitch

The url is tied to the name of the package. It would be great if the name of the package included something like a build number that gets updated or uses a package hash in the build string. You can see an example of both in the build string for the [pytorch-cpu-feedstock](https://github.com/conda-forge/pytorch-cpu-feedstock/blob/93333de760d702aee276dcafeedc890458a00417/recipe/meta.yaml#L21). This ensures that packages of the same version do not get confused with the same url.