[grid] Make distributor pick up session requests from the queue only if the grid is not full - #8940

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Description

Add a feature to pick up new session requests from the new session queue only if the grid is not busy.

Motivation and Context

Currently, the Distributor will pick up requests from the queue immediately as soon as they arrive and if the Grid is busy then it will initiate a retry. Ideally, the Distributor should check if there are any new requests and if the Grid can handle the new request and accordingly poll the new session queue. New session queue is actually a staging area for the new requests. The changes address this.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• I have read the contributing document.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.