Feature Request: Add an option to specify the depth of `--scan-history`

`--scan-history` scans all revisions, but if the depth of the history is too large, it would take a long time to scan all revisions.
So how about adding an option to specify the depth of revisions.

For example,

```
$ git secrets --scan-history --scan-history-depth 10 .
```

Thank you.

Start by locating the command-line handling for --scan-history and the code that traverses revisions. Trace how scan-history currently selects revisions, then check the existing CLI test coverage before defining the expected behavior. Done means the example --scan-history-depth 10 invocation limits scanning to the requested history depth.

Written by the indexing model from the issue text.