component AP gateway: fix headers case in signature: headers where not lower-cased in `headers` field of signature data, resulting in signature being rejected by Pleroma (but it was working with Mastodon). Also add `Content-Type` header. rel 371

ARG REVISION
FROM libervia/web:${REVISION:-dev}

LABEL maintainer="Goffi <tmp_dockerfiles@goffi.org>"

ARG DEBIAN_FRONTEND=noninteractive

USER root

COPY --chown=root:root libervia.conf /etc/libervia.conf

WORKDIR /home/libervia
USER libervia