feat(indexer): skip blobs indexing when there is skip-blobs flag

What does this MR do and why?

Related: gitlab#557397

This change adds a new command-line option called --skip-blobs that allows users to skip indexing file contents while still indexing commit information.

The main modifications include:

• Adding a new flag --skip-blobs to the command-line interface
• Moving an existing test function to a different location in the file for better organization
• Creating a new test that verifies the skip-blobs functionality works correctly - it confirms that when this option is used, commits are still indexed but file contents are ignored
• Updating the core indexing logic to check this flag and conditionally skip blob indexing when requested

This flag can be set from Rails when the setting elasticsearch_code_scope is disabled.

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.