Add size_bytes and index_file_count in the zoekt_repositories table

What does this MR do and why?

Add two columns index_file_count and size_bytes to store the repository zoekt file counts and size respectively. We will get these values in the callback for each successful index operation. These values will be used later on for better index assignments.

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Before	After

How to set up and validate locally

• Make sure zoekt is configured.
• Add a new commit to any project in the namespace for which Zoekt is enabled.
• Make sure that the Search::Zoekt::Repository record for the project has these values set index_file_count and size_bytes

Related to #477228 (closed)