docs: clarify DO_NOT_TRACK values for GitHub CLI telemetry opt-out

[BaconMan1168]

Why:

Closes: #45957

The page says any falsy value disables telemetry, then introduces DO_NOT_TRACK. That reads as if DO_NOT_TRACK accepts any falsy or truthy value, but the CLI only honors 1 or true.

What's being changed (if available, include any code snippets, screenshots, or gifs):

In github-cli-telemetry.md, one sentence added after the DO_NOT_TRACK mention: unlike GH_TELEMETRY, DO_NOT_TRACK only disables telemetry when set to 1 or true, and other values such as yes or enabled have no effect.

Source for the behavior: ParseTelemetryState in cli/cli internal/telemetry/telemetry.go, which lowercases and trims the value and disables telemetry only for 1 or true.

Check off the following:

• A subject matter expert (SME) has reviewed the technical accuracy of the content in this PR. In most cases, the author can be the SME. Open source contributions may require an SME review from GitHub staff.
• The changes in this PR meet the docs fundamentals that are required for all content.
• All CI checks are passing and the changes look good in the review environment.

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Table of review links

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Source	Review	Production	What Changed
github-cli/github-cli/github-cli-telemetry.md	fpt ghec ghes@ 3.22 3.21 3.20 3.19 3.18 3.17	fpt ghec ghes@ 3.22 3.21 3.20 3.19 3.18 3.17

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[subatoi]

Thank you for opening a PR for this, but since this hasn't been approved for a contribution yet, I'm going to close this out. You can read more about contributing to the GitHub docs here