Add causes parameter to fail and use it for extension tags

[fmeum]

By passing the Starlark representation of a module extension tag to the new causes parameter of fail, module extensions can generate less verbose and helpful error messages on user errors.

Before:

ERROR: Traceback (most recent call last):
	File "/home/user/.cache/bazel/_bazel_user/466e6feac151a1e22847383f4e503361/external/gazelle~override/internal/bzlmod/go_deps.bzl", line 165, column 21, in _go_deps_impl
		fail("Multiple overrides defined for Go module path \"{}\" in module \"{}\".".format(override_tag.path, module.name))
Error in fail: Multiple overrides defined for Go module path "github.com/stretchr/testify" in module "gazelle_bcr_tests".

After:

ERROR: go_deps: Multiple overrides defined for Go module path "github.com/stretchr/testify" in module "gazelle_bcr_tests".
Causes:	
	bazel_module_tag in file "<root>/MODULE.bazel", line 33, column 25, with value:
		go_deps.gazelle_override(
		    path = "github.com/stretchr/testify",
		    directives = ["gazelle:go_naming_convention go_default_library"],
		)
	bazel_module_tag in file "<root>/MODULE.bazel", line 39, column 25, with value:
		go_deps.gazelle_override(
		    path = "github.com/stretchr/testify",
		    directives = ["gazelle:go_naming_convention import"],
		)

Fixes #17375
Work towards #16763