use .env for server address in example app

[jdivock-stripe]

What it says on the tin… 

• Updates RN and server to pull API_URL from env variable and wil also look for API_URL_ANDROID due to it's differing emulator localhost mapping
• Moved api key and url env variables into CI project settings
• Got homebrew step from Configure Detox to cache Taps and Homebrew cache shaving ~8m from build times!
• bumped CI container size to medium+ in an effort to improve builds times

Fixes:
#50

Chips away at #43

Before:

After:

Android is roughly as happy (or sad) as it was before:

FAIL  e2e/app.e2e.js (421.002 s)
  Payments
    ✓ Connect and disconnect (17674 ms)
    ✕ Install required update and connect (206962 ms)
    ✓ Change discovery method to bluetooth proximity (9754 ms)
    ✓ Change discovery method to Internet (9820 ms)
    ✓ Collect card payment (33334 ms)
    ✕ Store card via readReusableCard (40610 ms)
    ✕ Store card via SetupIntent (40367 ms)
    ✓ In-Person Refund failed due to unsupported country (26945 ms)
    ○ skipped Required update impossible due to low battery

iOS is the same

FAIL  e2e/app.e2e.js (275.68 s)
  Payments
    ✓ Connect and disconnect (15753 ms)
    ✓ Install required update and connect (29102 ms)
    ✓ Change discovery method to bluetooth proximity (10929 ms)
    ✓ Change discovery method to Internet (10980 ms)
    ✓ Collect card payment (37770 ms)
    ✕ Store card via readReusableCard (38377 ms)
    ✕ Store card via SetupIntent (35426 ms)
    ✕ In-Person Refund failed due to unsupported country (49366 ms)
    ○ skipped Required update impossible due to low batter

[jdivock-stripe]

Adding the steps to start the local sever even though it's not in use (yet)

[jdivock-stripe]

this is a duplicate step as setting up the executor attaches the workspaces and costs another minute or so