cst: Downgrade error logs to debug

Recently added error logs do not take into account sleep aborted and
other shutdown related errors. Since the logs print exception details
which are already logged down the call chain, and the new logs are for
debugging hang in chunk read path, the new logs are downgraded to debug
level in this change.

(cherry picked from commit 9aa7caf)

src/v/cloud_storage/segment_chunk_api.cc

@@ -220,7 +220,7 @@ ss::future<segment_chunk::handle_t> segment_chunks::hydrate_chunk(
         }
     } catch (const std::exception& ex) {
         vlog(
-          _ctxlog.error,
+          _ctxlog.debug,
           "Failed to hydrate chunk start {}, error: {}",
           chunk_start,
           ex.what());

src/v/cloud_storage/segment_chunk_data_source.cc

@@ -107,7 +107,7 @@ ss::future<> chunk_data_source_impl::load_stream_for_chunk(
     } catch (...) {
         eptr = std::current_exception();
         vlog(
-          _ctxlog.error,
+          _ctxlog.debug,
           "Hydrating chunk {} failed with error {}",
           chunk_start,
           eptr);