Add request_id field to the log deletion API

[afarresg]

Describe the bug
As of right now, Loki doesn't seem to support size-based retention policies (#7927 is in progress), so we have implemented a script that monitors the size of a Kubernetes persistent volume and sends log deletion requests to remove the oldest logs. We essentially send a deletion request to /loki/api/v1/delete and then wait until the latest request is marked as processed.

It would be interesting if the API could return a field like request_id when sending the request so upon fetching the list of deletion requests one could safely track the actual status. Right now, these are the fields that represent a request:

{
  "request_id": "[...]",
  "start_time": [...],
  "end_time": [...],
  "query": "[...]",
  "status": "[...]",
  "created_at": [...]
},

To Reproduce
Steps to reproduce the behavior:

1. Send a POST request to /loki/api/v1/delete with the range of time
2. Send a GET request to list all the requests

Expected behavior
A field request_id is returned when POSTing, and this same field is available when GETing.

Environment:

• Infrastructure: Kubernetes
• Deployment tool: Helm