More detailed event store spec failure message

What does this MR do and why?

This changes the event store publish_event rspec matcher failure message to be more descriptive.

When there's no event matching, instead of getting the published events in an array, like:

expected Pages::PageDeployedEvent with {:project_id=>242, :namespace_id=>719, :root_namespace_id=>719} to be published, but got [#<Pages::PageDeletedEvent data: {:project_id=>242, :namespace_id=>719, :root_namespace_id=>719}>]

We'll get all published events in a list format:

expected Pages::PageDeployedEvent with {:project_id=>243, :namespace_id=>721, :root_namespace_id=>721} to be published, but only the following events were published:
- #<Pages::PageDeletedEvent data: {:project_id=>243, :namespace_id=>721, :root_namespace_id=>721}>

And, when no event was published, instead of an empty array:

expected Pages::PageDeployedEvent with {:project_id=>242, :namespace_id=>719, :root_namespace_id=>719} to be published, but got []

we'll get the description that no events were published:

expected Pages::PageDeployedEvent with {:project_id=>244, :namespace_id=>723, :root_namespace_id=>723} to be published, but no events were published.

Also, inspecting an event doesn't show its memory address to have a more concise information in the screen.

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