[4.5.0]

Added

• Asset proxying for generating pre-signed S3 URLs through proxy endpoints GET /collections/{collectionId}/items/{itemId}/assets/{assetKey} and GET /collections/{collectionId}/assets/{assetKey}.
• Environment variables ASSET_PROXY_BUCKET_OPTION, ASSET_PROXY_BUCKET_LIST, and
  ASSET_PROXY_URL_EXPIRY to configure asset proxying.

Changed

• When asset proxying is enabled, when a STAC Item or Collection is served, asset S3 hrefs
  are replaced with proxy endpoint URLs and the original S3 URLs are preserved in
  alternate.s3.href using the Alternate Assets Extension.

Fixed

• When using the _filter parameter, the combined filter was returned in the next link
  body. This had the correct semantics, but the size of the filter would grow by one
  and nesting each pagination request, as the _filter was repeatedly added to body.