feat(search-coordinator): Add initial scaffolding.

[Bill-hbrhbr]

Description

Checklist

• The PR satisfies the contribution guidelines.
• This is a breaking change and that has been indicated in the PR title, OR this isn't a
  breaking change.
• Necessary docs have been updated, OR no docs need to be updated.

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[LinZhihao-723]

As discussed offline, this PR is too large and we should break it into small ones to tight the scope for better decision making. I would propose the following:

• search_job_submitter with only the trait. The implementation depends on TDL. We can implement it for Spider client, but leave it with todo!.
• job_handle implemention on top of search_job_submitter.
  • We probably need to split this mod even further (splitting into smaller PRs). Use todo! to define the interface first.
• coordination implemention on top of job_handle.
• bin implementation.

Assume tdl becomes available in parallel, the binary itself should be able to serve search jobs. We then plan to add the Python side and deployment integration.

[LinZhihao-723]

I'm not sure whether we need all of the schema changes in this file. In the formal PR, we should document why we need to add a new column.

[LinZhihao-723]

Why?