Replace argument with the project_id flag [3/4]

This MR is a part of gitlab#336100 (closed)

This MR changes the arguments for the indexer: Instead of providing project_id as the required one, this changes it to be a named argument which can be omitted when needed. For example, group wikis that do not have project_id

From:

Usage: %s [ --version | [--blob-type=(blob|wiki_blob)] [--skip-commits] [--search-curation] [--full-path=<full-path>] [--timeout=<timeout>] [--visbility-level=<visbility-level>] [--repository-access-level=<repository-access-level>] [--wiki-access-level=<wiki-access-level>] <project-id> <repo-path> ]

To:

Usage: %s [ --version | [--blob-type=(blob|wiki_blob)] [--project-id=<ID>] [--skip-commits] [--search-curation] [--full-path=<full-path>] [--timeout=<timeout>] [--visbility-level=<visbility-level>] [--repository-access-level=<repository-access-level>] [--wiki-access-level=<wiki-access-level>] <repo-path> ]