feat(lambda-tiler): show the first pipeline as the preview instead of a broken image

[blacha]

Motivation

We need preview URLS so that we can display a list of DEM layers in the layer viewer

Modification

Adds support for pipelines for preview url generation when viewing the landing page.

Checklist

If not applicable, provide explanation of why.

• [ ] Tests updated
• [ ] Docs updated
• [ ] Issue linked in Title