feat(clientIDKey): support clientIDKey config

[BillXiang]

Fixes: #27

Motivation

some API used by cubefs-dashboard need clientIDKey when authentication is enabled

Modifications

add clientIDKey config

Types of changes

• New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] Bugfix (non-breaking change which fixes an issue)
• [ ] Documentation Update (if none of the other choices apply)
• [ ] So on...

Verifying this change

• [ ] Make sure that the change passes the testing checks.

This change is a trivial rework / code cleanup without any test coverage.

(or)

This change is already covered by existing tests, such as (please describe tests).

(or)

This change added tests and can be verified as follows:

(example:)

• This can be verified in development debugging
• This can be realized in a mocked environment, like a test cluster consisting in docker

(or)

This change MUST reappear in online clusters, or occur in that specific scenarios.

Does this pull request potentially affect one of the following parts:

Documentation

• [ ] doc
• [ ] doc-required
• [ ] doc-not-needed
• [ ] doc-complete

Review Expection

• [ ] in-two-days
• [ ] weekly
• [ ] free-time
• whenever

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