test: Add e2e tests for multiple installs in the same cluster

[jonstacks]

What

Adds CI tests that we can build off over time for testing installing multiple ngrok operators into a single cluster. Now that we have multiple installs working, we want to run tests to make sure we don't break that functionality.

How

Adds a new e2e-multi-namespace that runs after the regular e2e tests.

Breaking Changes

No, this is testing only.

[Copilot]

Pull request overview

This PR adds end-to-end tests for validating multiple ngrok operator installations in a single Kubernetes cluster, ensuring the multi-namespace functionality works correctly and doesn't regress over time.

Key changes:

• New e2e-tests-multi-ns make target for running multi-namespace tests
• New e2e-multi-namespace GitHub Actions job that runs after regular e2e tests
• Comprehensive test suite in tests/chainsaw-multi-ns/ covering sanity checks and operator registration for two operators in separate namespaces

Reviewed changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
tools/make/test.mk	Adds new e2e-tests-multi-ns make target to run chainsaw tests from the chainsaw-multi-ns directory
tests/chainsaw-multi-ns/sanity-checks/*.yaml	Validates that both operators (a and b) and their agents are running, and that ingress classes exist in respective namespaces
tests/chainsaw-multi-ns/operator-registration/chainsaw-test.yaml	Tests that both operators successfully register with ngrok and receive proper IDs
tests/chainsaw-multi-ns/README.md	Documents the test structure, prerequisites, and guidelines for writing new multi-namespace tests
.github/workflows/ci.yaml	Adds new CI job for multi-namespace e2e testing with proper concurrency control and cleanup
.github/actions/build-and-test/action.yaml	Updates KIND version from v0.26.0 to v0.30.0

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 49.15%. Comparing base (029fd83) to head (9792438).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #737      +/-   ##
==========================================
+ Coverage   49.13%   49.15%   +0.01%     
==========================================
  Files          96       96              
  Lines       10604    10604              
==========================================
+ Hits         5210     5212       +2     
+ Misses       5037     5030       -7     
- Partials      357      362       +5     

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