Fail on manifest duplicate packages

[ericlchen1]

Currently having duplicate packages in your manifest will cause bad behavior when actually using those packages.
Fail when duplicate packages are seen in the manifest file.

Ex: 2 dpkg packages in packagesand bazel run @bullseye//:lock

packages:
  - "dpkg"
  - "dpkg"

Without changes and duplicates, the lock passes, but will have duplicate dependencies which leads to errors when actually using the package "@bullseye//dpkg".

				{
					"key": "libcrypt1_1-4.4.18-4_amd64",
					"name": "libcrypt1",
					"version": "1:4.4.18-4"
				},
				...
				{
					"key": "libcrypt1_1-4.4.18-4_amd64",
					"name": "libcrypt1",
					"version": "1:4.4.18-4"
				},

ERROR: /home/eric/.cache/bazel/_bazel_eric/0dc37115db8d04cb9adf89231812a093/external/bullseye/dpkg/amd64/BUILD.bazel:18:10: Label '@bullseye//libcrypt1/amd64:amd64' is duplicated in the 'srcs' attribute of rule 'amd64'

With PR:

ERROR: An error occurred during the fetch of repository 'bullseye_resolution':
   Traceback (most recent call last):
        File "/home/eric/Documents/rules_distroless/apt/private/resolve.bzl", line 82, column 21, in _deb_resolve_impl
                fail("Duplicate package, {}. Please remove it from your manifest".format(dep_constraint))
Error in fail: Duplicate package, dpkg. Please remove it from your manifest
ERROR: /home/eric/Documents/rules_distroless/WORKSPACE.bazel:29:10: fetching deb_resolve rule //external:bullseye_resolution: Traceback (most recent call last):
        File "/home/eric/Documents/rules_distroless/apt/private/resolve.bzl", line 82, column 21, in _deb_resolve_impl
                fail("Duplicate package, {}. Please remove it from your manifest".format(dep_constraint))
Error in fail: Duplicate package, dpkg. Please remove it from your manifest