Missing documentation about [env] section

[flxo]

Problem

With #9175 a new feature landed:

An [env] section in the cargo configuration to pass additional env variables to all program invocations does by cargo.

From the PR:

[env]
FOOBAR = "Apple"
PATH_TO_SOME_TOOL = { value = "bin/tool", relative = true }
USERNAME = { value = "test_user", force = true }

This information is missing in the Cargo Reference/Configuration section.

Possible Solution(s)

Add [env] to the Configuration format section and to the Configuration Keys

[ehuss]

Closing per #9297 (comment).