Fix TSDB head struct dump on querier error (#8379)

* Fix TSDB head struct dump on querier error
Signed-off-by: NMarco Pracucci <marco@pracucci.com>

* Added mint/maxt to RangeHead.String()
Signed-off-by: NMarco Pracucci <marco@pracucci.com>

tsdb/head.go

@@ -1010,6 +1010,13 @@ func (h *RangeHead) Meta() BlockMeta {
 	}
 }
 
+// String returns an human readable representation of the range head. It's important to
+// keep this function in order to avoid the struct dump when the head is stringified in
+// errors or logs.
+func (h *RangeHead) String() string {
+	return fmt.Sprintf("range head (mint: %d, maxt: %d)", h.MinTime(), h.MaxTime())
+}
+
 // initAppender is a helper to initialize the time bounds of the head
 // upon the first sample it receives.
 type initAppender struct {
@@ -1492,6 +1499,13 @@ func (h *Head) Close() error {
 	return errs.Err()
 }
 
+// String returns an human readable representation of the TSDB head. It's important to
+// keep this function in order to avoid the struct dump when the head is stringified in
+// errors or logs.
+func (h *Head) String() string {
+	return "head"
+}
+
 type headChunkReader struct {
 	head       *Head
 	mint, maxt int64