fix #1102: feign-form-spring relocated under io.github.openfeign

[DidierLoiseau]

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Fixed #1102 and aligns feign-form-spring with the rest of OpenFeign.

~Leaving the exclusion for commons-io for now since it still has vulnerabilities in versions < 2.14 (See also #1098), which is still a transitive dependency of feign-form-spring:13.5 (via commons-fileupload:1.5).~

Edit: I just realized that excluding commons-io but removing the direct dependency on commons-fileupload will not work for end users, as they actually need the former for the latter.

Previously it was still there because of the explicit dependency on commons-fileupload (the exclusions were a bit useless, actually), and users were getting version 2.11 (with the CVE mentioned in #1098). It will still be the case. The only dependencies that actually change in this PR are feign-form and feign-form-spring (checked with dependency:list on the starter module after mvn install).

Note that there is also an explicit dependency on version 2.17, but only with test scope. You might as well make it a compile-time dependency so that users get the version with the CVE fix…