Change instance ID and execution ID for an UUID

**Is your feature request related to a problem? Please describe.**
It is a new feature to have the generated ID to be UUID instead of a hash of the user and the created_at time

**Describe the solution you'd like**
To have randomly generated UUIDs

**Describe alternatives you've considered**
None

**Additional context**
None. But maybe we want to have an UUID to report back to the user and use it as an external_id, but keep an integer as the internal id and primary key of the table to have a better database storage and disk size consumption.

The issue names instance IDs, execution IDs, UUID generation, and possible internal database IDs, but no files or tests. Start by locating where these IDs are generated and used in persistence and the REST API; clarify whether UUIDs replace existing identifiers or are added as external IDs, then define tests covering the agreed behavior.

Written by the indexing model from the issue text.