pw_kvs: Apply config pattern; configure log level

- Add PW_KVS_LOG_LEVEL to the pw_kvs config file and update code to
  use it.
- Define a pw_kvs:config facade that be used to override configuration
  values.
- Set up the empty "$dir_pw_build:empty" target that all modules use as
  their default configuration backend via the
  pw_build_DEFAULT_MODULE_CONFIGURATION variable.

Change-Id: Idf54d93678ffbd65e9e02a10454df4479f73827a
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/21240
Reviewed-by: David Rogers <davidrogers@google.com>
Reviewed-by: Armando Montanez <amontanez@google.com>
Commit-Queue: Wyatt Hepler <hepler@google.com>
diff --git a/pw_kvs/public/pw_kvs/flash_memory.h b/pw_kvs/public/pw_kvs/flash_memory.h
index 0590e56..d1864b4 100644
--- a/pw_kvs/public/pw_kvs/flash_memory.h
+++ b/pw_kvs/public/pw_kvs/flash_memory.h
@@ -18,7 +18,7 @@
 #include <initializer_list>
 #include <span>
 
-#include "pw_assert/assert.h"
+#include "pw_assert/light.h"
 #include "pw_kvs/alignment.h"
 #include "pw_status/status.h"
 #include "pw_status/status_with_size.h"
@@ -48,7 +48,7 @@
         start_address_(start_address),
         start_sector_(sector_start),
         erased_memory_content_(erased_memory_content) {
-    PW_DCHECK_UINT_NE(alignment_, 0);
+    PW_ASSERT(alignment_ != 0u);
   }
 
   virtual ~FlashMemory() = default;