Paginate balances endpoint

[moisses89]

What is needed?

Currently we have some long balances lists, the idea of this issue is to paginate this list to split the list in several pages.

Related issues

https://github.com/safe-global/safe-transaction-service/issues/1408

Current endpoint

/api/v1/safes/{safe-address}/balances/

New endpoint

GET /api/v2/safes/{safe-address}/balances/

Response

Paginated list of tokens

{
 "count": <num_tokens>, 
 "next": "...", 
"previous": "...",
"results": [...]
}