Make redis imports optional (#549)

**Related Issue(s):**

- #548 

**Description:**

- Made redis imports contingent on redis env var being enabled 

**PR Checklist:**

- [x] Code is formatted and linted (run `pre-commit run --all-files`)
- [x] Tests pass (run `make test`)
- [x] Documentation has been updated to reflect changes, if applicable
- [x] Changes are added to the changelog

Author: jonhealy1

CHANGELOG.md

@@ -16,6 +16,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - Fix incorrect min/max date formatting in `apply_datetime_filter` for `POST` requests. [#539](https://github.com/stac-utils/stac-fastapi-elasticsearch-opensearch/pull/539)
 - Fixed datetime filtering for .0Z milliseconds to preserve precision in apply_filter_datetime, ensuring only items exactly within the specified range are returned. [#535](https://github.com/stac-utils/stac-fastapi-elasticsearch-opensearch/pull/535)
 - Normalize datetime in POST /search requests to match GET /search behavior. [#543](https://github.com/stac-utils/stac-fastapi-elasticsearch-opensearch/pull/543)
+- Fix optional Redis support in core.py. [#549](https://github.com/stac-utils/stac-fastapi-elasticsearch-opensearch/pull/549)
 
 ### Removed
 

stac_fastapi/core/stac_fastapi/core/core.py

@@ -24,7 +24,6 @@
 from stac_fastapi.core.base_settings import ApiBaseSettings
 from stac_fastapi.core.datetime_utils import format_datetime_range
 from stac_fastapi.core.models.links import PagingLinks
-from stac_fastapi.core.redis_utils import redis_pagination_links
 from stac_fastapi.core.serializers import CollectionSerializer, ItemSerializer
 from stac_fastapi.core.session import Session
 from stac_fastapi.core.utilities import filter_fields, get_bool_env
@@ -426,6 +425,8 @@ async def all_collections(
         ]
 
         if redis_enable:
+            from stac_fastapi.core.redis_utils import redis_pagination_links
+
             await redis_pagination_links(
                 current_url=str(request.url),
                 token=token,
@@ -904,6 +905,8 @@ async def post_search(
         links.extend(collection_links)
 
         if redis_enable:
+            from stac_fastapi.core.redis_utils import redis_pagination_links
+
             await redis_pagination_links(
                 current_url=str(request.url),
                 token=token_param,