PeerCert shouldn't be URLEncoded when provided through a header

[exalate-issue-sync]

When the AM GW is behind a reverse proxy, the client certificate can be provided through a HTTP Header to the GW.

Currently AM considere this cert as URLEncoded as it is the behaviour of NGnix but it is not a standard behaviour.

We have to follow standard format and provide a way to manage the NGinx one.

[Orejiro]

Hello,

I just had something to keep in mind. After the resolution of this issue APIM JWT Policy should be adapted accordingly (https://github.com/gravitee-io/gravitee-policy-jwt#specific-configuration-for-confirmation-method-validation).