Update Cache and Mail ENV Variable Names and Config Files to Match Modern Laravel

[allella]

Our .env.example is using the deprecated MAIL_DRIVER.  It seems MAIL_MAILER is the way since Laravel 7.
Our config/mail.php still references the old value.

(DONE via #755 ) Our .env.example is using the deprecated CACHE_DRIVER. CACHE_STORE seems to be the suggested variable in modern Laravel.
Our config/cache.php still references the old value.

[allella]

Also, .env.ci could probably benefit from setting

MAIL_MAILER=log

[allella]

@kevindees I gather you may have been asking about CACHE_DRIVER in #750 (comment) related to this issue?

I see the .env.example says # Setting the cache driver to "array" will disable the cache. It's currently set to FILE, so I guess if we don't see a reason to have a cache in the .env.ci, then

CACHE_DRIVER=array

would make sense there.

[allella]

#755 updated the CACHE_DRIVER.

We still could address the change from MAIL_DRIVER to MAIL_MAILER (since Laravel 7).

Are there any other outdated .env variables or tweaks we'd like to make to the examples and .env files?