Add pre-computed tracking information to security report schema

Add a schema for pre-calculated tracking fingerprint values as part of https://gitlab.com/groups/gitlab-org/-/epics/4690.

Calculated tracking values should be added in-line with each position in the tracking data.

For example, given analyzer-provided tracking information for a vulnerability in a security report:

"tracking": {
  "type": "source",
  "positions": [
    { "file": "path/to/file1.ext", "line_start": 10, "line_end": 20 },
    { "file": "path/to/file2.ext", "line_start": 10, "line_end": 20 },
    { "file": "path/to/file3.ext", "line_start": 10, "line_end": 20 }
  ]
}

Calculated tracking values should be inserted inline into each position object:

"tracking": {
  "type": "source",
  "positions": [
    { "file": "path/to/file1.ext", "line_start": 10, "line_end": 20, "fingerprints": { "scope+offset": "path/to/file1.ext|scope1|scope2:offset" } },
    { "file": "path/to/file2.ext", "line_start": 10, "line_end": 20, "fingerprints": { "scope+offset": "path/to/file2.ext|scope1|scope2:offset" } },
    { "file": "path/to/file3.ext", "line_start": 10, "line_end": 20, "fingerprints": { "scope+offset": "path/to/file3.ext|scope1|scope2:offset" } }
  ]
}