Use C++20 ends_with() for suffix checking in GatewaySupervisor

[Copilot]

Addresses code review feedback to modernize string suffix checking in GatewaySupervisor.cc.

Changes

• Replace manual character-by-character suffix comparison with C++20 std::string::ends_with("END---")
• Remove redundant dumpStr.size() >= 6 check (handled internally by ends_with())
• Introduce const reference to avoid repeated member access
• Fix logic inversion: original incorrectly checked for suffix absence

Before:

if(remoteGatewayApp.config_dump.size() > 10 &&
   (remoteGatewayApp.config_dump[remoteGatewayApp.config_dump.size() - 1] != '-' ||
    remoteGatewayApp.config_dump[remoteGatewayApp.config_dump.size() - 2] != '-' ||
    // ... 4 more comparisons
    ))

After:

const std::string& dumpStr = remoteGatewayApp.config_dump;
if(dumpStr.size() > 10 && dumpStr.ends_with("END---"))

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