[FlyteCTL Feature] Sandbox and demo teardown command should better give instruction to unset env var

[honnix]

Describe the feature/command for FlyteCTL

After running start command for sandbox and demo, flytectl prints the instruction to set FLYTECTL_CONFIG env var pointing to a config file made for the sandbox/demo; however the teardown command does not tell users to unset the env var. So very often, users end up with having FLYTECTL_CONFIG pointing to an invalid config file, and that makes any other flytectl commands not being executed correctly towards a production setup.

Provide a possible output or UX example

Teardown command could print out something like: please run unset FLYTECTL_CONFIG to clean up the environment variable.

Are you sure this issue hasn't been raised already?

• Yes

Have you read the Code of Conduct?

• Yes