fix: shorten custom data in cloud init files

[christinalau0]

Reason for Change:

Previously, deploying mixed clusters (linux + windows nodes) with azuredisk-csi-driver addon hit custom data too long error:
Custom data in OSProfile must be in Base64 encoding and with a maximum length of 87380 characters.

• This PR shortens variable names in cloud init scripts, reducing custom data length.
• ci: Test suites previously set EnableTelemetry to true by default, which caused the CSE to be longer. This PR sets EnableTelemetry to false by default.
• ci: Fix featureflag nil pointers now that the EnableTelemetry feature flag is no longer set by default.

Issue Fixed:

Credit Where Due:

Does this change contain code from or inspired by another project?

• No
• Yes

If "Yes," did you notify that project's maintainers and provide attribution?

• No
• Yes

Requirements:

• uses conventional commit messages
• includes documentation
• adds unit tests
• tested upgrade from previous version

Notes:

[christinalau0]

/azp run

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