pass signing public key as arg

Earthfile

@@ -33,6 +33,7 @@ ARG ISO_NAME=installer
 ARG K8S_DISTRIBUTION
 ARG CUSTOM_TAG
 ARG CLUSTERCONFIG
+ARG SIGNING_PUBLIC_KEY
 ARG ARCH
 ARG DISABLE_SELINUX=true
 ARG CIS_HARDENING=true
@@ -312,7 +313,10 @@ build-uki-iso:
     COPY --platform=linux/${ARCH} +luet/luet /overlay/luet
 
     COPY --if-exists content-*/*.zst /overlay/opt/spectrocloud/content/
-    COPY --if-exists public-key /overlay/.signing-public-key
+    #check if signing public key is passed in
+    IF [ "$SIGNING_PUBLIC_KEY" != "" ]
+        COPY --if-exists "$SIGNING_PUBLIC_KEY" /overlay/.signing-public-key
+    END
     RUN if [ -n "$(ls /overlay/opt/spectrocloud/content/*.zst 2>/dev/null)" ]; then \
         for file in /overlay/opt/spectrocloud/content/*.zst; do \
             split --bytes=3GB --numeric-suffixes "$file" /overlay/opt/spectrocloud/content/$(basename "$file")_part; \
@@ -364,7 +368,11 @@ build-iso:
     COPY overlay/files-iso/ /overlay/
     COPY --if-exists user-data /overlay/files-iso/config.yaml
     COPY --if-exists content-*/*.zst /overlay/opt/spectrocloud/content/
-    COPY --if-exists public-key /overlay/.signing-public-key
+
+    #check if signing public key is passed in
+    IF [ "$SIGNING_PUBLIC_KEY" != "" ]
+        COPY --if-exists "$SIGNING_PUBLIC_KEY" /overlay/.signing-public-key
+    END
     RUN if [ -n "$(ls /overlay/opt/spectrocloud/content/*.zst 2>/dev/null)" ]; then \
         for file in /overlay/opt/spectrocloud/content/*.zst; do \
             split --bytes=3GB --numeric-suffixes "$file" /overlay/opt/spectrocloud/content/$(basename "$file")_part; \