Allow Filter annotations to be stacked in a third one

[ggerbaud]

Fixes #4767

[CLAassistant]

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[jameskleeh]

@ggerbaud This needs a test. Should probably live in HttpFilterSpec

[ggerbaud]

@jameskleeh Ok, so I add some tests and dit the changes on client and server filters

[jameskleeh]

@ggerbaud Appreciate the effort here! I think the test needs to also reflect the original issue, which was the use of multiple annotations on the container annotation.

[ggerbaud]

@jameskleeh My issue was related to a use case (grouping multiple filters behind one annotation to simplify thier declaration) but the test illustrated the technical reason (filters were searched only in direct annotations, not through stereotypes).
But I add more tests to illustrate all of this.

I also add tests with two annotations filters directly on the client.
Note that in this case, annotation declaration order matters because the clients are the same except for filters. If they have the same first filter, they end up with the same key, due to this line.

[jameskleeh]

Thank you for your contribution!