[api] Start observation from address

[olemis]

[POST] /api/transactions/history/from/{address}/observation

Should start observation of the transactions that transfer fund from the address . Should affect result of the [GET] /api/transactions/history/from/{address} .

Errors:

* `409 Conflict` : transactions from the  address  are already observed.

Python implementation

@api.route('/transactions/history/from/<string:address>/observation', methods=['POST'])
def add_history_from_address(address):
    """
    Starts observation of the transactions that transfer fund from the address 
    """
    
    result = add_transaction_observation_from_address(address)
    
    # if successfully stored in observation list, return a plain 200
    if "error" in result:
        return make_response(jsonify(build_error(result["error"])), result["status"])
    else:
        return ""