Append explanatory string - (multiple participants) to Contribution amount_level when contribution is paying for multiple participants

If a user registers for multiple participants - we create one contribution record which covers fee for multiple participants. However, when an admin views that contribution record - it displays their individual fee_level along with a grand total amount. This is confusing.

EXAMPLE: I registered for myself for Single fee level ($50) and 2nd participant for Family ($200). When I view the contribution records the AMOUNT columns shows:
"$ 250.00 - Single" - which doesn't make sense.

We can improve this by appending the constant string "(multiple participants)" to the civicrm_contribution.amount_level string whenever we are inserting a contribution record that covers multiple participants.

EXAMPLE:

• amount_level would be "Single (multiple participants)"
• display in AMOUNT column of contribution selector would be "$ 250.00 - Single (multiple participants)"