Summary:
Loading vector LSM index chunks could take a significant amount of time.
To speed up this process, we could load them concurrently using a thread pool.

This diff implements concurrent load for vector LSM.

Also introduced vector LSM failure status.
Once a single operation fails in the vector LSM, the vector LSM is moved to the failed status.
Jira: DB-13626

Test Plan: vector_lsm-test

Reviewers: mbautin, aleksandr.ponomarenko, arybochkin

Reviewed By: mbautin

Subscribers: ybase

Tags: #jenkins-ready

Differential Revision: https://phorge.dev.yugabyte.com/D39230