Allow switching languages without editing leetcode.toml

[gotlougit]

This may be a more personal use-case thing, but I like to write Leetcode solutions in C++ and Rust, and having to edit the leetcode.toml file to do so is pretty inconvenient. It would be nice to have a flag which could tell the program to write the solution in the X language, maybe like this:

leetcode e 1234 --lang rust

Perhaps this may become a bit complicated when running leetcode t 1234, but we could rely on the default language set in leetcode.toml for that and have the user pass the flag every time they wish to use the non-default languages.

I would like to have a discussion if this could be a valid feature that could be added to make the CLI experience better