switched to tokio tasks

[vishalkrishnads]

Fixes #652.

Description

• Rewrote object_store_sync() & run_local_sync() in server's sync.rs to use tokio tasks but with same function signature. Updated the invoking code to match.

• Rewrote init_scheduler() in server's storage/retention.rs to use tokio tasks but with same function signature. Updated the invoking code to match.

---

This PR has:

• been tested to ensure log ingestion and log query works.
• added comments explaining the "why" and the intent of the code wherever would not be obvious for an unfamiliar reader.
• added documentation for new or modified features or behaviors.

[github-actions]

CLA Assistant Lite bot All contributors have signed the CLA ✍️ ✅

[vishalkrishnads]

I have read the CLA Document and I hereby sign the CLA

[nitisht]

@vishalkrishnads are you able to verify if the server is running and accepting events after this change?

[vishalkrishnads]

the server runs but isn't accepting requests.

[nitisht]

the server runs but isn't accepting requests.

I see, so thats why tests are failing. Would you take a deeper look at what is going on?

[vishalkrishnads]

yes sure, i'll look into it. please give me a bit more time.

[nitisht]

yes sure, i'll look into it. please give me a bit more time.

Sure @vishalkrishnads . Please let us know if you need any help.

[vishalkrishnads]

this is kind of confusing. in this commit, all checks except the indentation one were passing. however, as I corrected it, the distributed docker compose test started failing. @nitisht any help would be appreciated.