Reset primary keys after swapping events tables

What does this MR do?

This MR ensures primary key values of events are properly reset after swapping the tables. Without doing so event IDs will start with 1, possibly producing duplicate key violations. I forgot to add this to the events migration cleanup but it's absolutely crucial we include this in the very first 10.0 deploy as otherwise GitLab.com will run into issues.

cc @rspeicher @jarka

Does this MR meet the acceptance criteria?

• Review
  • Has been reviewed by Backend
  • Has been reviewed by Database
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together