ci: allow forks to have different names

When the fork of the "docs" repository is called something else, we need to refer to it by the real name to successfully perform the replacement for merge request pipelines.

Use some bash and CI_MERGE_REQUEST_SOURCE_PROJECT_PATH to find the bare name of the project. This works because the variable is re-interpolated by bash during job execution.

Signed-off-by: Zygmunt Krynicki zygmunt.krynicki@huawei.com