Add a link to the VsCode Extension Pack download in the in product developer center

[jpvajda]

To help users find the extension easier, let's add a link the the marketplace to download the extension in the developer center.

AC

0. Check if there are any security issues with linking out from the developer center.

1. Ad a link to the [marketplace download page]https://marketplace.visualstudio.com/items?itemName=new-relic.new-relic-extension-pack) is added to the developer center.

2. One thing to consider when linking to an external site from NR1 is that the Referer header could contain the entire URL, and those URLs contain a ton of data. To keep Microsoft from consuming our customer data, we’ll want to make sure the Referrer-Policy (oddly enough, they spelled ‘Referrer’ correctly here) is set properly. That probably looks like either Referrer-Policy: no-referrer or Referrer-Policy: origin