Add endpoint to generate readable logs in observer

Current situation

Currently, there is no way to access readable logs outside of opentf-ctl.

Desired outcome

We need to add an endpoint in observer to generate readable logs in order fir Squash TM to get logs at T time (pseudo real-time logs)

Probably something like GET /workflows/{workflow_id}/logs, maybe with pagination or query options to specify the expected detail level.

The required credentials are get on workflows. The usual namespace access rights check are performed.

Specificity

This issue needs to be done before september 30th in order to do the next par in TM 8.0. (If not done, we'll see to include it in 9.0)