Create the new project 'git-repo-manifests'

The 'git-repo-manifests' project will hold manifest files which can be
used with the git-repo program to clone multiple projects at once.

git-repo also known as repo is developed hand-in-hand with Gerrit by
Google.  https://gerrit.googlesource.com/git-repo

Manifest files are XML documents used to specify multiple git
repositories that are associated with each other. This will allow being
able to pull down all git repositories associated with a master project. For
example the Ironic project has multiple git repositories associated with
it. For example:
    - openstack/bifrost
    - openstack/coreos-image-builder
    - openstack/ironic
    - openstack/ironic-inspector
    - openstack/ironic-lib
    - openstack/ironic-python-agent
    - openstack/ironic-specs
    - openstack/ironic-webclient
    - openstack/python-dracclient
    - openstack/python-ironic-inspector-client
    - openstack/python-ironicclient

With a correct manifest file and git-repo installed could do the
following to check out all the repositories:
 $ repo init -u https://review.openstack.org/openstack/git-repo-manifests -m ironic
 $ repo sync -c

This will be purely optional for usage by developers.

Change-Id: Ib685484dc0a237131c16952301ac55d7b6356a03

gerrit/acls/openstack/git-repo-manifests.config

@@ -0,0 +1,15 @@
+[access "refs/heads/*"]
+abandon = group git-repo-manifests-core
+create = group git-repo-manifests-release
+label-Code-Review = -2..+2 group git-repo-manifests-core
+label-Workflow = -1..+1 group git-repo-manifests-core
+
+[access "refs/tags/*"]
+pushSignedTag = group git-repo-manifests-release
+
+[receive]
+requireChangeId = true
+requireContributorAgreement = true
+
+[submit]
+mergeContent = true

gerrit/projects.yaml

@@ -1033,6 +1033,8 @@
     - oslo
 - project: openstack/gantt
   description: Common scheduler for OpenStack.
+- project: openstack/git-repo-manifests
+  description: Clone multiple OpenStack repos as a group
 - project: openstack/glance
   docimpact-group: openstack-manuals
   description: OpenStack Image Management (Glance)

zuul/layout.yaml

@@ -4363,6 +4363,11 @@ projects:
       - name: merge-check
       - name: noop-jobs
 
+  - name: openstack/git-repo-manifests
+    template:
+      - name: merge-check
+      - name: noop-jobs
+
   - name: openstack/governance
     template:
       - name: merge-check