Alpine: Install rsvg-convert package if it's available

The `rsvg-convert` binary is shipped in the `rsvg-convert` package since
Alpine 3.17.

STACK=alpine
RELEASE=3.2, 3.1.13

Fixes: #239

Author: tarleb

alpine/Dockerfile

@@ -95,8 +95,9 @@ COPY --from=alpine-builder \
 
 # Additional packages frequently used during conversions
 # NOTE: `libsrvg`, pandoc uses `rsvg-convert` for working with svg images.
-RUN apk --no-cache add \
-        librsvg
+# FIXME: Alpine 3.17 and later ships the binary in the rsvg-convert package.
+RUN apk --no-cache add librsvg; \
+    apk --no-cache add rsvg-convert || true
 
 # LaTeX #################################################################
 FROM alpine-core as alpine-latex