X-Reva-Secret header missing error is used for wrong situatoin.

[shokri-navid]

I found that the X-Reva-Secret header missing error is raised because of two situations:

1- when the Reva version is under 1.19.0: in these versions, the NextCould manager of Reva does not add the X-Reva-Secret header to the HTTP request.

2- when X-Reva-Secret is sent from Reva side to the Nextcloud with the wrong value.

in the first case, it seems it is better to provide a hint about the Reva version.
in the second case, it seems it is better that we return another error message that indicates the wrong value.

[MahdiBaghbani]

@michielbdejong @navid-shokri is it fixed or we have to fix it? is it even necessary anymore?