Add tenv linter (#5801)

This is the contrib counterpart of
open-telemetry/opentelemetry-go#5524, adding the
tenv linter.

Co-authored-by: Robert Pająk <pellared@hotmail.com>
Co-authored-by: Tyler Yahn <MrAlias@users.noreply.github.com>

.golangci.yml

@@ -22,6 +22,7 @@ linters:
     - misspell
     - revive
     - staticcheck
+    - tenv
     - typecheck
     - unconvert
     - unparam