proxy unstable routing behavior for routes that match multiple rules

[rhafer]

Turns out that the config changes in #4461 cause some unstable behavior for routes that match multiple rules 😱. E.g. we have:

                {                                 
                    Endpoint:    "/app/list",
                    Backend:     "http://localhost:9140",
                    Unprotected: true,
                },
                {
                    Endpoint: "/app/", // /app or /apps? ocdav only handles /apps
                    Backend:  "http://localhost:9140",
                },

And now requests on /app/list/ sometimes go through and sometimes fail. (Not this is not exactly a new bug in the code, it just seems that we didn't have overlapping rules of the same type before. I'll open a new issue for that and try to come up with a quick fix. (We might also temporary revert this PR).

Originally posted by @rhafer in #4461 (comment)

[rhafer]

Turns out that this is cause by the route iterating of the endpoints of the rules for a specific type in random order. So sometimes the /app rule is evaluated first and sometimes /app/list (See: https://github.com/owncloud/ocis/blob/master/services/proxy/pkg/router/router.go#L208)

[rhafer]

Even though the quick fix is merged. I'd like to keep this issue open for now. As the fix is somewhat inefficient. E.g. it is sorting the endpoints over and over again (ideally this would only happen once, at startup.
Also it might need adjustments for other types of rules than PrefixRoute