feat: delta for code scan [IDE-448]

[ShawkyZ]

Description

This PR adds the following:

• delta package that introduces a flow for calculating deltas. Entrypoint is: delta_finder.go
• delta_finder has two public methods. Enrich (for enriching current analysis results with the IsNew flag).
  Diff: For returning only the diff between current branch analysis vs base branch analysis.
• delta_finder relies on: Enricher, Differ and Matcher. Differ for determining the diff between two scan results. Matcher for matching two issue types and Enricher for enriching results if necessary with Ids or IsNew.
• Matcher implementation for matching code analysis results bases on the implementation of (code-issue-identity) https://github.com/snyk/code-issue-identity
• new settings option enableSnykDelta.
• Initial version of cloning base branch and scanning it (There will be followup PR for caching results)
• Base branch choice is hardcoded (Follow-up PR for base scan option persisting/loading)

Current scan flow should work as before if the option enableDeltaFindings is not set.

Checklist

• Tests added and all succeed
• Linted
• README.md updated, if user-facing
• License file updated, if new 3rd-party dependency is introduced

🚨After having merged, please update the CLI go.mod to pull in latest language server.

Screenshots / GIFs

Visuals that may help the reviewer. Please add screenshots for any UI change. GIFs are most welcome!