feat: kepub conversions

Working *.epub to *.kepub.epub file conversions when
using a Kobo reader. Updated docker file to include
`kepubify` to convert to kepub. If not available the
file is just sent without conversion.

dockerfile

@@ -1,6 +1,19 @@
 # Dockerfile.distroless
 FROM golang:1.22 as base
 
+RUN
+# Download and install kepubify
+RUN wget https://github.com/pgaskin/kepubify/releases/download/v4.0.4/kepubify-linux-64bit && \
+    mv kepubify-linux-64bit /usr/local/bin/kepubify && \
+    chmod +x /usr/local/bin/kepubify
+
+# Download and install kindlegen
+RUN wget https://web.archive.org/web/20150803131026if_/https://kindlegen.s3.amazonaws.com/kindlegen_linux_2.6_i386_v2_9.tar.gz && \
+    mkdir kindlegen && \
+    tar xvf kindlegen_linux_2.6_i386_v2_9.tar.gz --directory kindlegen && \
+    cp kindlegen/kindlegen /usr/local/bin/kindlegen && \
+    chmod +x /usr/local/bin/kindlegen
+
 WORKDIR /src/kobo-opds-proxy/app/
 
 COPY go.mod .
@@ -15,6 +28,8 @@ RUN CGO_ENABLED=0 GOOS=linux GOARCH=amd64 go build .
 
 FROM gcr.io/distroless/static
 
+COPY --from=base /usr/local/bin/kepubify /usr/local/bin/kepubify
+COPY --from=base /usr/local/bin/kindlegen /usr/local/bin/kindlegen
 COPY --from=base /src/kobo-opds-proxy/app/kobo-opds-proxy .
 
 CMD ["./kobo-opds-proxy"]