Update GhoStewardV2.sol

[marczeller]

• Allowed GSM fees to be lowered

• Allowed GSM exposure & borrow cap to be changed both ways

[height]

Link Height tasks by mentioning a task ID in the pull request title or commit messages, or description and comments with the keyword link (e.g. "Link T-123").

💡Tip: You can also use "Close T-X" to automatically close a task when the pull request is merged.

[marczeller]

governance discussions:

https://governance.aave.com/t/arfc-gho-stewards/16466/10?u=marczeller

[JoaquinBattilana]

implementation looking good but can you please update the tests on TestGhoStewardV2.t.sol please?
They are failing because there are checks for the contract to be reverting when lowering the parameters
for example:

  function testRevertUpdateGhoBorrowCapIfValueLowerThanCurrent() public {
    uint256 oldBorrowCap = 1e6;
    _setGhoBorrowCapViaConfigurator(oldBorrowCap);
    vm.prank(RISK_COUNCIL);
    vm.expectRevert('INVALID_BORROW_CAP_UPDATE');
    GHO_STEWARD_V2.updateGhoBorrowCap(oldBorrowCap - 1);
  }

Also it would be good to have successful tests when lowering the parameters, and reverting when updating a value lower than allowed.

[miguelmtzinf]

Please, update IGhoStewardV2 natspec docs to reflect the new changes.

[miguelmtzinf]

Closes #401

[marczeller]

@JoaquinBattilana did a separated PR for tests: #403

[miguelmtzinf]

Merged to a dedicated branch to consolidate all changes and trigger tests