Add max retransmit and shred insert slot (#15475)

docs/src/developing/clients/jsonrpc-api.md

@@ -42,6 +42,8 @@ gives a convenient interface for the RPC methods.
 - [getInflationRate](jsonrpc-api.md#getinflationrate)
 - [getLargestAccounts](jsonrpc-api.md#getlargestaccounts)
 - [getLeaderSchedule](jsonrpc-api.md#getleaderschedule)
+- [getMaxRetransmitSlot](jsonrpc-api.md#getmaxretransmitslot)
+- [getMaxShredInsertSlot](jsonrpc-api.md#getmaxshredinsertslot)
 - [getMinimumBalanceForRentExemption](jsonrpc-api.md#getminimumbalanceforrentexemption)
 - [getMultipleAccounts](jsonrpc-api.md#getmultipleaccounts)
 - [getProgramAccounts](jsonrpc-api.md#getprogramaccounts)
@@ -1612,6 +1614,50 @@ Result:
 }
 ```
 
+### getMaxRetransmitSlot
+
+Get the max slot seen from retransmit stage.
+
+#### Results:
+
+- `<u64>` - Slot
+
+#### Example:
+
+Request:
+```bash
+curl http://localhost:8899 -X POST -H "Content-Type: application/json" -d '
+  {"jsonrpc":"2.0","id":1, "method":"getMaxRetransmitSlot"}
+'
+```
+
+Result:
+```json
+{"jsonrpc":"2.0","result":1234,"id":1}
+```
+
+### getMaxShredInsertSlot
+
+Get the max slot seen from after shred insert.
+
+#### Results:
+
+- `<u64>` - Slot
+
+#### Example:
+
+Request:
+```bash
+curl http://localhost:8899 -X POST -H "Content-Type: application/json" -d '
+  {"jsonrpc":"2.0","id":1, "method":"getMaxShredInsertSlot"}
+'
+```
+
+Result:
+```json
+{"jsonrpc":"2.0","result":1234,"id":1}
+```
+
 ### getMinimumBalanceForRentExemption
 
 Returns minimum balance required to make account rent exempt.