Nix flake templates for easy dev environments

To initialize (where ${ENV} is listed in the table below):

nix flake init --template github:the-nix-way/dev-templates#${ENV}

Here's an example (for the rust template):

nix flake init --template github:the-nix-way/dev-templates#rust

Available templates:

Language/framework/tool	Template
Dhall	dhall
Elixir	elixir
Gleam	gleam
Go 1.17	go1_17
Go 1.18	go1_18
Java	java
Kotlin	kotlin
Nix	nix
Node.js	node
Rust	rust
Scala	scala
Zig	zig