fix(contracts): OZ-L2-L05 Lack of Event Emissions

[zimpha]

Purpose or design rationale of this PR

This PR fix the bug (L-05 Lack of Event Emissions) reported by OpenZeppelin. The following are the details:

Throughout the codebase, several instances were identified where events should be emitted.

• When Whitelist is deployed, the owner is set by the constructor. Because owner is not set using _transferOwnership , the OwnershipTransferred event is not emitted.
• The updateMessenger function does not emit an event upon the successful update of the L2ScrollMessenger address.
• The L2GatewayRouter does not emit an event when setting defaultERC20Gateway in the initialize function.

Consider emitting the OwnershipTransferred event, as well as an event when the address of the L2ScrollMessenger gets updated on the L2MessageQueue contract. Furthermore, consider emitting the SetERC20Gateway event when the L2GatewayRouter is initialized. Emitting events provides a way for external integrations to track changes being made to the contract configuration by external integrations. This is especially important for monitoring operations and proper incident response, particularly with regard to trusted entities with special privileges.

PR title

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• feat: A new feature
• fix: A bug fix
• perf: A code change that improves performance
• refactor: A code change that doesn't fix a bug, or add a feature, or improves performance
• style: Changes that do not affect the meaning of the code (white-space, formatting, missing semi-colons, etc)
• test: Adding missing tests or correcting existing tests

Deployment tag versioning

Has tag in common/version.go been updated?

• No, this PR doesn't involve a new deployment, git tag, docker image tag
• Yes

Breaking change label

Does this PR have the breaking-change label?

• No, this PR is not a breaking change
• Yes

[github-actions]

LCOV of commit b3c3afa during Contracts #1167

Summary coverage rate:
  lines......: 52.1% (894 of 1715 lines)
  functions..: 69.5% (203 of 292 functions)
  branches...: no data found

Files changed coverage rate: n/a