Source Square: implement oauth2 java-part

[midavadim]

square implement oauth2 (java part)

https://developer.squareup.com/reference/square/oauth-api/authorize

=========== JAVA PART ================

1. Approve access from customer side using:
   client_id
   scope
   https://connect.squareup.com/oauth2/authorize?client_id=sq0idb-...&scope=CUSTOMERS_WRITE+MERCHANT_PROFILE_READ+EMPLOYEES_READ+PAYMENTS_READ+CUSTOMERS_READ+TIMECARDS_READ+ORDERS_READ&session=False&state=82201dd8d83d23cc8a48caf52b

   https://connect.squareup.com/oauth2/authorize?client_id=sq0idp-...&scope=ITEMS_READ+CUSTOMERS_READ&session=False&state=82201dd8d83d23cc8a48caf52b

2. Get redirect url with 'code':

   https://airbyte.io/?code=sq0cg-...&response_type=code&state=82201dd8d83d23cc8a48caf52b#_=_

3. Obtain token using

   curl https://connect.squareup.com/oauth2/token
   -X POST
   -H 'Square-Version: 2021-09-15'
   -H 'Content-Type: application/json'
   -d '{
   "client_id": "sq0idp-...",
   "client_secret": "sq0csp-...",
   "grant_type": "authorization_code",
   "code": "sq0cgp-...",
   "scopes": [
   "ITEMS_READ",
   "MERCHANT_PROFILE_READ",
   "EMPLOYEES_READ",
   "PAYMENTS_READ",
   "CUSTOMERS_READ",
   "TIMECARDS_READ",
   "ORDERS_READ"
   ],
   }'

   RESPONSE:
   {
   "access_token": "EAAAEPF...",
   "token_type": "bearer",
   "expires_at": "2021-11-04T16:15:50Z",
   "merchant_id": "ML2PMZQ...",
   "refresh_token": "EQAAEPhF.....", <======
   "short_lived": false
   }

   OAuth access tokens expire after 30 days.
   Refresh tokens do not expire.

============== PYTHON PART =====================

4. API requests using access_token.

5. Refresh access_token using refresh_token:

   curl https://connect.squareup.com/oauth2/token
   -X POST
   -H 'Square-Version: 2021-09-15'
   -H 'Content-Type: application/json'
   -d '{
   "client_id": "sq0idp-...",
   "client_secret": "sq0csp-...",
   "grant_type": "refresh_token",
   "refresh_token": "EQAAEPhF...",
   "scopes": [
   "CUSTOMERS_READ"
   ]
   }'

   RESPONSE:
   {
   "access_token": "EAAAEB7I_...",
   "token_type": "bearer",
   "expires_at": "2021-11-04T18:55:43Z",
   "merchant_id": "ML2PMZQ5....,
   "refresh_token": "EQAAEPhF...",
   "short_lived": false
   }

[etsybaev]

To check
#6842

[artem1205]

Implemented in #6842