Add new Containerfile.tests to be used by openshift.release

Description:
- this new Containerfile.tests will be used by the CI/CD system
  to run all the needed unit tests
- it will be used as a build_root so that we are able to use the
  latest golang since there is no OCP builder image for go 1.21 yet

Containerfile.tests

@@ -0,0 +1,26 @@
+#
+# Copyright (c) 2023 Red Hat, Inc.
+#
+# Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
+# in compliance with the License. You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software distributed under the License
+# is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
+# or implied. See the License for the specific language governing permissions and limitations under
+# the License.
+#
+
+FROM docker.io/golang:1.21 AS builder
+WORKDIR /go/src/github.com/openshift-kni/oran-o2ims
+COPY . .
+
+# Install ginkgo & mockgen.
+RUN go install github.com/onsi/ginkgo/v2/ginkgo@$(go list -f '{{.Version}}' -m github.com/onsi/ginkgo/v2) && \
+  go install go.uber.org/mock/[email protected]
+
+# Install golangci-lint.
+RUN curl -sSfL https://raw.githubusercontent.com/golangci/golangci-lint/master/install.sh | sh -s -- -b $(go env GOPATH)/bin v1.55.2 && \
+  golangci-lint --version
+