Add Nextalign

At Richard's request to facilitate integration of Nextalign into the
ncov builds.

Dockerfile

@@ -180,6 +180,11 @@ COPY --from=builder \
 COPY --from=builder /build/vcftools/built/bin/    /usr/local/bin/
 COPY --from=builder /build/vcftools/built/share/  /usr/local/share/
 
+# Add Nextalign
+RUN curl -fsSL https://github.com/neherlab/nextalign/releases/latest/download/nextalign-Linux-x86_64 \
+        -o /usr/local/bin/nextalign \
+ && chmod a+rx /usr/local/bin/nextalign
+
 # Ensure all container users can execute these programs
 RUN chmod a+rX /usr/local/bin/* /usr/local/libexec/*