Multi-env warn of branch mismatch.

**Is your feature request related to a problem? Please describe.**
More of an inconvenience. Might just be me though. But I usually don't remember to amplify env checkout branch.

**Describe the solution you'd like**
If you are on a different branch to the env currently used by amplify, warn the user during an amplify push.

**Describe alternatives you've considered**
Updating my bash config to call both commands at once.

**Additional context**
N/A