Add: [GS] Allow to set max loan for each company separately (#11224)

src/economy_type.h

@@ -200,6 +200,8 @@ struct PriceBaseSpec {
 static const int LOAN_INTERVAL = 10000;
 /** The size of loan for a new company, in British Pounds! */
 static const int64_t INITIAL_LOAN = 100000;
+/** The max amount possible to configure for a max loan of a company. */
+static const int64_t MAX_LOAN_LIMIT = 2000000000;
 
 /**
  * Maximum inflation (including fractional part) without causing overflows in int64_t price computations.