fix: handle SSL certificate verification failures in curl install script (closes #28044)

[MORDEHAI BOTBIKA (botbikamordehai2-sketch)]

What

Fix issue #28044 where az bicep install fails with SSLCertVerificationError when downloading from aka.ms. The root cause is that the urlopen calls in the install script do not respect the system's trusted CA certificates, especially on Windows with corporate proxies or security software that inject self-signed certificates.

Fix

The script now creates an SSL context using ssl.create_default_context(), which uses the system's default CA bundle. If that fails or is incomplete (e.g., on some Windows setups), it falls back to using the certifi package's CA bundle if available. As a last resort, it can be run with --insecure-like behavior by setting an environment variable AZURE_CLI_DISABLE_SSL_VERIFICATION (not enabled by default). This change ensures the script can download necessary files even when a self-signed certificate is in the chain, while preserving security when possible.

Closes #28044

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Thank you for your contribution MORDEHAI BOTBIKA (@botbikamordehai2-sketch)! We will review the pull request and get back to you soon.

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[Yong Zhang (yonzhan)]

bicep