Authentication for Generic EventSource

[whynowy]

Is your feature request related to a problem? Please describe.
An authentication approach for Generic EventSource.

Describe the solution you'd like
An optional selectKeySelector to indicate the authentication credential in Generic EventSource spec, use the secret as Bearer token in the header for authentication.

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Additional context
Add any other context or screenshots about the feature request here.

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