Improve validate-origin

If we set the main.git.upstreamRepoURL then we need to check that one
for the presence of the branch and not whatever is configured as the
origin remote.

Tested as follows:

- Working upstreamRepoURL:

    ❯ yq -r '.main.git.repoUpstreamURL // (.main.git.repoUpstreamURL = "")' values-global.yaml
    https://github.com/mbaldessari/industrial-edge
    ❯ make validate-origin
    make -f common/Makefile validate-origin
    make[1]: Entering directory '/home/michele/Engineering/cloud-patterns/industrial-edge'
    Checking repository:
    Upstream URL set to: https://github.com/mbaldessari/industrial-edge
      https://github.com/mbaldessari/industrial-edge - branch 'for-max-s3-kafka-fix': OK
    make[1]: Leaving directory '/home/michele/Engineering/cloud-patterns/industrial-edge'

- upstreamRepoURL without the branch:

    ❯ yq -r '.main.git.repoUpstreamURL // (.main.git.repoUpstreamURL = "")' values-global.yaml
    https://github.com/mamurak/industrial-edge
    ❯ make validate-origin
    make -f common/Makefile validate-origin
    make[1]: Entering directory '/home/michele/Engineering/cloud-patterns/industrial-edge'
    Checking repository:
    Upstream URL set to: https://github.com/mamurak/industrial-edge
      https://github.com/mamurak/industrial-edge - branch 'for-max-s3-kafka-fix': NOT FOUND
    make[1]: *** [common/Makefile:138: validate-origin] Error 1
    make[1]: Leaving directory '/home/michele/Engineering/cloud-patterns/industrial-edge'
    make: *** [Makefile:24: validate-origin] Error 2

- No repoUpstreamURL set:

    ❯ yq -r '.main.git.repoUpstreamURL // (.main.git.repoUpstreamURL = "")' values-global.yaml
    ❯
    ❯ make validate-origin
    make -f common/Makefile validate-origin
    make[1]: Entering directory '/home/michele/Engineering/cloud-patterns/industrial-edge'
    Checking repository:
      https://github.com/mbaldessari/industrial-edge.git - branch 'for-max-s3-kafka-fix': OK
    make[1]: Leaving directory '/home/michele/Engineering/cloud-patterns/industrial-edge'

Author: mbaldessari

Makefile

@@ -129,12 +129,22 @@ token-kubeconfig: ## Create a local ~/.kube/config with password (not usually ne
 
 # We only check the remote ssh git branch's existance if we're not running inside a container
 # as getting ssh auth working inside a container seems a bit brittle
+# If the main repoUpstreamURL field is set, then we need to check against
+# that and not target_repo
 .PHONY: validate-origin
 validate-origin: ## verify the git origin is available
 	@echo "Checking repository:"
-	@echo -n "  $(TARGET_REPO) - branch '$(TARGET_BRANCH)': "
-	@git ls-remote --exit-code --heads $(TARGET_REPO) $(TARGET_BRANCH) >/dev/null &&\
-		echo "OK" || (echo "NOT FOUND"; exit 1)
+	$(eval UPSTREAMURL := $(shell yq -r '.main.git.repoUpstreamURL // (.main.git.repoUpstreamURL = "")' values-global.yaml))
+	@if [ -z "$(UPSTREAMURL)" ]; then\
+		echo -n "  $(TARGET_REPO) - branch '$(TARGET_BRANCH)': ";\
+		git ls-remote --exit-code --heads $(TARGET_REPO) $(TARGET_BRANCH) >/dev/null &&\
+			echo "OK" || (echo "NOT FOUND"; exit 1);\
+	else\
+		echo "Upstream URL set to: $(UPSTREAMURL)";\
+		echo -n "  $(UPSTREAMURL) - branch '$(TARGET_BRANCH)': ";\
+		git ls-remote --exit-code --heads $(UPSTREAMURL) $(TARGET_BRANCH) >/dev/null &&\
+			echo "OK" || (echo "NOT FOUND"; exit 1);\
+	fi
 
 .PHONY: validate-cluster
 validate-cluster: ## Do some cluster validations before installing