Exclude non-training clients from cse

[yanchengnv]

Fixes #4562056

Description

The CCWF's cross-site-eval workflow (CSE) assumes all evaluatees have local models. However, depending on the config of the Swarm Learning workflow (usually before CSE) of the job, some clients may only be aggregators and don't train. In this case, the client that is not a trainer won't be able to submit local model, which causes the CSE to fail.

This PR fixes this issue by checking the client against the training clients list of Swarm Learning workflow. Only training clients will be treated as evaluatees.

Types of changes

• Non-breaking change (fix or new feature that would not break existing functionality).
• Breaking change (fix or new feature that would cause existing functionality to change).
• New tests added to cover the changes.
• Quick tests passed locally by running ./runtest.sh.
• In-line docstrings updated.
• Documentation updated.

[SYangster]

Nice fix, LGTM