feat: introduce roaring bitmap to inverted index (#219)

proto/greptime/v1/index/inverted_index.proto

@@ -63,6 +63,9 @@ message InvertedIndexMeta {
 
     // Statistical information about the tag's inverted index.
     InvertedIndexStats stats = 8;
+
+    // The type of bitmap used for indexing.
+    BitmapType bitmap_type = 9;
 }
 
 // InvertedIndexStats provides statistical data on a tag's inverted index.
@@ -79,3 +82,9 @@ message InvertedIndexStats {
     // The maximum value found within the tag's column, encoded as bytes.
     bytes max_value = 4;
 }
+
+// BitmapType defines the type of bitmap used for indexing.
+enum BitmapType {
+    BitVec = 0;
+    Roaring = 1;
+}