Enhance `genHTMLFragment` to Include Anchor Tags in Environment Variable Table Output

[mike-weiner]

Please provide a description of this PR:

Resolves https://github.com/istio/istio.io/issues/16552.

This PR adds anchor link tags to the tool that generates the environment variable tables for the documentation of each CLI.

I tested this change by running make build followed by ./out/darwin_arm64/pilot-discovery collateral --html_fragment_with_front_matter.

This change outputs HTML in the following format:

<tr id='ambient-enable-multi-network'>
<td><a href='#ambient-enable-multi-network'><code>AMBIENT_ENABLE_MULTI_NETWORK</code></a></td>
<td>Boolean</td>
<td><code>false</code></td>
<td>If true, the multi-network functionality will be enabled.</td>
</tr>

I then took the HTML that was generated and ran in locally through the website via make serve from the istio.io repository.

[istio-policy-bot]

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[mike-weiner]

/retest-required