fix(governance): replace multisig to operator

[ahramy]

AXE-4769

• replace multisig to operator in the service governance contract.
• Whether the address is a multisig is or not is not really relevant to the contract anymore.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 98.54%. Comparing base (b53530c) to head (283041a).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #185 +/- ## ======================================= Coverage 98.54% 98.54% ======================================= Files 48 48 Lines 758 758 Branches 157 157 ======================================= Hits 747 747 Misses 1 1 Partials 10 10 ```

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