feat: allow to disable version check

[ParminderParmar]

Reason for change

In airgapped (offline) environments, the application attempts to check for the latest version online and fails with a network error. This causes unnecessary errors in logs and potential confusion for users.

This PR introduces an environment variable ALLOW_LATEST_VERSION_CHECK (default: True) that allows administrators to disable the version check when running in restricted environments.

Relevant issue: #7175

Code change

LATEST_VERSION_CHECK = get_bool_env('ALLOW_LATEST_VERSION_CHECK', True)

Screenshots
N/A (no visible UI changes).

Rollout strategy

• Controlled via the ALLOW_LATEST_VERSION_CHECK environment variable.
• Default behavior remains unchanged (True), so existing deployments are not affected.
• Airgapped users can explicitly set ALLOW_LATEST_VERSION_CHECK=False to disable online version checks.

Testing

• Verified in an airgapped server by setting ALLOW_LATEST_VERSION_CHECK=False → no more failed requests.
• Verified in a normal environment with default setting (True) → version check continues to work.

Risks

• Minimal. Default behavior is preserved.
• Only risk is that some users may disable version checking unintentionally, but this is explicit via env var.

General notes
This PR provides a safe and configurable way to run Label Studio in offline/airgapped environments without spurious errors.
It addresses a common pain point for enterprise users operating without internet access.

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