Switch database cleaner strategy from `:trunction` to `:deletion`

What does this MR do?

Switch DatabaseCleaner strategy to improve performance on machines with slow I/O and prevent:

An error occurred in a `before(:suite)` hook.
Failure/Error: DatabaseCleaner.clean_with(:truncation)

ActiveRecord::QueryCanceled:
  PG::QueryCanceled: ERROR:  canceling statement due to statement timeout

Does this MR meet the acceptance criteria?

Conformity

• I have included changelog trailers, or none are needed. (Does this MR need a changelog?)
• I have added/updated documentation, or it's not needed. (Is documentation required?)
• I have properly separated EE content from FOSS, or this MR is FOSS only. (Where should EE code go?)
• I have added information for database reviewers in the MR description, or it's not needed. (Does this MR have database related changes?)
• I have self-reviewed this MR per code review guidelines.
• This MR does not harm performance, or I have asked a reviewer to help assess the performance impact. (Merge request performance guidelines)
• I have followed the style guides.
• This change is backwards compatible across updates, or this does not apply.

Fix #336733 (closed)