fix: do not open listen events socket in webhook

[CrazyHackGUT]

What does this PR do?

Fixes a memory leak caused by using webhook engine by incorrect get_master_event parameters.

What issues does this PR fix or reference?

Memory leak in EventPublisher

Previous Behavior

get_master_event returns an object with opened pull-socket, which was not required for the publication of events, what causes memory leak in EventPublisher: EventPublisher sends a message for another process, but webhook doesn't even plan to read them.

New Behavior

get_master_event don't opens a pull-socket.

Merge requirements satisfied?

[NOTICE] Bug fixes or features added to Salt require tests.

• Docs
• Changelog - https://docs.saltproject.io/en/master/topics/development/changelog.html
• Tests written/updated

Commits signed with GPG?

No

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[twangboy]

Please create a changelog and a test for this

[CrazyHackGUT]

Added a changelog entry (I used PR number as issue number)
Wrote simple test for testing this change, but I guess a test for the whole webhook for master + minion would be more appropriate here.