[grid] Integrated NewSessionQueuer with the Router.

[pujagani]

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Description

Integrate NewSessionQueuer with the Router.

Motivation and Context

All new session requests will be routed via the NewSessionQueuer and added to the NewSessionQueue. Distributor will pick up the session requests and create the session.

The changes include:

1. Make the Router aware of the NewSessionQueuer. Update the RouterServer.
2. Update the Distributor by removing endpoint to create a new session. It should be routed via the NewSessionQueuer.
3. Distributor tests are updated to use Either. Asserts are updated based on each test.
4. Remove CreateSession class.
5. Update the Distributor newsession() method to return Either.

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.

[CLAassistant]

All committers have signed the CLA.

[diemol]

Thank you!