Allow user to pass a list of commands for one single stage (#4934)

* Allow list type in STAGE_DEFINITION scheme and join(cmd) if list

* Remove join in Stage.__init__ and update test

* Loop over commands in cmd_run

* Improve logging of stage.run with detailed by command

* Fix test based on log message

* Update command logging with >

* Add tests for multi lines command

* Update > to $ in stage command log to prevent confusion with > operator

* Fix PR review about test: single quote and read_text

* tests: unify/clarify tests

Co-authored-by: Ruslan Kuprieiev <[email protected]>

scripts/schema/dvc-yaml.json

@@ -102,8 +102,8 @@
           "type": "object",
           "properties": {
             "cmd": {
-              "type": "string",
-              "description": "Command to run"
+              "type": ["string", "array"],
+              "description": "Command(s) to run"
             },
             "wdir": {
               "type": "string",