After successfully switching extra array serialization to JSON codec we should migrate existing Events and rewrite the values from echo.event_extra column.

Acceptance criteria:

• a script that will run through echo_event table, and for each row will try to deserialize it with PHP unserialize, and then store the value as JsonCodec::serialize().
• execute script on prod envs
• once all rows are migrated update Event::deserializeExtra() and remove the use of unserialize() function.