rproxy: pass WebDAV methods on (closes #278)

rproxy now passes PROPFIND, PROPPATCH, MKCOL, COPY, MOVE, REPORT,
SEARCH, LOCK and UNLOCK to discriminator instead of answering 405, so
Nextcloud's Files app and sync client work. The Core Rule Set's 911100
still refuses them wherever no app's exclusions allow them.

Model: opus-5-5

internal/rproxy/rproxy.go

@@ -51,7 +51,9 @@ const ownEndpointPrefix = "/_sww/"
 
 // allowedMethods lists the methods rproxy passes on, as an Allow header gives
 // them. It answers any other method 405 itself.
-const allowedMethods = "GET, HEAD, POST, OPTIONS, PUT, DELETE, PATCH, QUERY"
+// The WebDAV ones are for Nextcloud.
+const allowedMethods = "GET, HEAD, POST, OPTIONS, PUT, DELETE, PATCH, QUERY, " +
+	"PROPFIND, PROPPATCH, MKCOL, COPY, MOVE, REPORT, SEARCH, LOCK, UNLOCK"
 
 // Params are what New needs.
 type Params struct {