feat: Add envd as a new language extension in github linguist

[VoVAllen]

Description

Example from tilt github-linguist/linguist#4831

[kemingy]

This should be done by https://github.com/tensorchord/envd-lsp

[kemingy]

It will be better if the vscode plugin can also modify the envd file icon.

[VoVAllen]

Not viable now. Github requires language popularity (grammar used in hundreds of repos held by different people), that envd doesn't satisfy yet.

[gaocegege]

https://github.com/github/linguist/blob/master/CONTRIBUTING.md#adding-an-extension-to-a-language

We try only to add languages once they have some usage on GitHub. In most cases we prefer that each new file extension be in use in at least 200 unique :user/:repo repositories before supporting them in Linguist (but see #5756 for a temporary change in the criteria).

[gaocegege]

Ref github-linguist/linguist#5756