docs(operator): add E2E test instructions, clarify task usage, and automate Chainsaw install

[olamide226]

• Added clear instructions for running Operator E2E and unit/integration tests in README
• Clarified that all operator task commands should be run from the project root
• Updated Taskfile to auto-install Chainsaw for local runs, skipping in CI

Ref: #1843

[Copilot]

Pull Request Overview

This PR enhances the operator documentation and testing setup by adding comprehensive test running instructions and automating tool installation. The changes improve developer experience by clarifying how to run different types of tests and ensuring required tools are available.

• Added detailed instructions for running both unit/integration and E2E tests
• Clarified that operator task commands should be run from project root
• Automated Chainsaw installation for local development while preserving CI behavior

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
cmd/thv-operator/Taskfile.yml	Added conditional Chainsaw auto-installation for local development
cmd/thv-operator/README.md	Added comprehensive test running instructions and prerequisites

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 46.70%. Comparing base (d525d2c) to head (1adef91).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1929      +/-   ##
==========================================
- Coverage   46.73%   46.70%   -0.03%     
==========================================
  Files         220      220              
  Lines       27378    27378              
==========================================
- Hits        12795    12788       -7     
- Misses      13604    13618      +14     
+ Partials      979      972       -7     

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