Add ability to disable the version conflict failure, instead we warn.

internal/bzlmod/go_deps.bzl

@@ -202,7 +202,7 @@ _go_repository_config = repository_rule(
     },
 )
 
-def fail_if_duplicate_modules_have_different_versions(version, previous, module_tag, module_name_to_go_dot_mod_label, go_works):
+def fail_on_version_conflict(version, previous, module_tag, module_name_to_go_dot_mod_label, go_works, fail_or_warn):
     """
     Check if duplicate modules have different versions, and fail with a useful error message if they do.
 
@@ -249,7 +249,12 @@ def fail_if_duplicate_modules_have_different_versions(version, previous, module_
         else:
             corrective_measure = "To correct this, run: go work sync."
 
-    fail("Multiple versions of {} found:\n - {} contains {}\n - {} contains {}.\n{}".format(module_tag.path, current_label, humanize_comparable_version(version), previous_label, humanize_comparable_version(previous.version), corrective_measure))
+    message = "Multiple versions of {} found:\n - {} contains {}\n - {} contains {}.\n{}".format(module_tag.path, current_label, humanize_comparable_version(version), previous_label, humanize_comparable_version(previous.version), corrective_measure)
+
+    if fail_or_warn:
+      fail(message)
+    else:
+      print(message)
 
 def _fail_if_not_root(module, from_file_tag):
     if module.is_root != True:
@@ -426,8 +431,10 @@ def _go_deps_impl(module_ctx):
             version = semver.to_comparable(raw_version)
             previous = paths.get(module_tag.path)
 
+            fail_or_warn = len([x for x in module.tags.from_file if x.fail_on_version_conflict == True ]) > 0
+
             # rather then failing, we could do MVS here, or some other heuristic
-            fail_if_duplicate_modules_have_different_versions(version, previous, module_tag, module_name_to_go_dot_mod_label, go_works)
+            fail_on_version_conflict(version, previous, module_tag, module_name_to_go_dot_mod_label, go_works, fail_or_warn)
             paths[module_tag.path] = struct(version = version, module_tag = module_tag)
 
             if module_tag.path not in module_resolutions or version > module_resolutions[module_tag.path].version:
@@ -606,6 +613,7 @@ _from_file_tag = tag_class(
     attrs = {
         "go_mod": attr.label(mandatory = False),
         "go_work": attr.label(mandatory = False),
+        "fail_on_version_conflict": attr.bool(default = True),
     },
 )