Updated Makefile to check and warn if az cli if unavailable in local

[vishalanarase]

What type of PR is this?
/kind feature

What this PR does / why we need it:
Adds a check-az-cli Makefile target that detects whether azure-cli (az) is on PATH, prints a clear warning with install instructions when it is not, and runs automatically before make tilt-up so developers are told to install Azure CLI before Tilt hits az (e.g. VNet peering with an AKS management cluster). Supports VERBOSE=1 make check-az-cli to print the resolved az path when present.
Removes the obsolete TODO in the Tiltfile now covered by the Makefile check. Updates the development guide and AGENTS.md to describe the behavior.

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #5291

Special notes for your reviewer:

TODOs:

• squashed commits
• includes documentation
• adds unit tests
• cherry-pick candidate

Release note:

make tilt-up now runs a check that warns when the Azure CLI (az) is not installed or not on PATH, with optional VERBOSE=1 on make check-az-cli to print the detected binary path.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 43.67%. Comparing base (50f20f4) to head (2302f6d).
⚠️ Report is 20 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #6177   +/-   ##
=======================================
  Coverage   43.66%   43.67%           
=======================================
  Files         289      289           
  Lines       25495    25495           
=======================================
+ Hits        11132    11134    +2     
+ Misses      13561    13559    -2     
  Partials      802      802           

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[willie-yao]

/assign

[vishalanarase]

/assign

[mboersma]

/lgtm

[k8s-ci-robot]

LGTM label has been added.

Details

Git tree hash: 0985a513cf55ef5e2cee732b9d23787ecd2207ad

[willie-yao]

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: willie-yao

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