Update remote ssh to use cdn hosted artifacts

[petetronic]

With installers now hosted on cdn.posit.com, we need to update the remote ssh template to point to the cdn and not github for release artifacts.

See:

1. https://github.com/posit-dev/positron/blob/main/product.json#L17

"serverDownloadUrlTemplate": "https://github.com/posit-dev/positron/releases/download/${version}/positron-reh-${os}-${arch}-${version}.tar.gz",

2. https://github.com/posit-dev/positron/blob/main/extensions/open-remote-ssh/src/serverSetup.ts#L38

const DEFAULT_DOWNLOAD_URL_TEMPLATE = 'https://github.com/posit-dev/positron/releases/download/${version}/positron-reh-${os}-${arch}-${version}.tar.gz';

3. https://github.com/posit-dev/positron/blob/main/extensions/open-remote-ssh/package.json#L80

"default": "https://github.com/posit-dev/positron/releases/download/${version}/positron-reh-${os}-${arch}-${version}.tar.gz"

The new template should be something like:

https://cdn.posit.co/positron/dailies/reh/${arch}/positron-reh-${os}-${arch}-${version}.tar.gz

[petetronic]

All builds should be in /dailies/... track to start, though stable monthly prereleases would be promoted to /prereleases/.... We would need a sense of editioning in the product if we were to further parameterize the URI template. I think we can start with dailies.