assets: Add Copyright and License for reuse compliance

Signed-off-by: Andrei Gherzan <andrei.gherzan@huawei.com>

assets/ostc-logo-small-loading.png.license

+# SPDX-FileCopyrightText: Huawei Inc.
+#
+# SPDX-License-Identifier: Apache-2.0

assets/ostc-logo-small.png.license

+# SPDX-FileCopyrightText: Huawei Inc.
+#
+# SPDX-License-Identifier: Apache-2.0