AE and AM job families should include their mid-market focus

Account Executive and Account Manager job families should now designate which market(s) they're focused on, such as Account Executives, Mid-market. I'm updating the respective job families pages as well as the team.yml file to reflect the change.

@jarmendariz's original message below:

We will no longer use just "account executive" or "account manager." Is there a way to remove those titles altogether so that it is not used in the handbook (roles page I guess) or in offer letters, etc.

cc @brittanyr