doc: add setTrieFlushInterval method (#26366)

debug: add setTrieFlushInterval method docs

docs/_rpc/ns-debug.md

@@ -387,6 +387,19 @@ Sets the rate of mutex profiling.
 | Console | `debug.setMutexProfileFraction(rate int)`                       |
 | RPC     | `{"method": "debug_setMutexProfileFraction", "params": [rate]}` |
 
+### debug_setTrieFlushInterval
+
+Configures how often in-memory state tries are persisted to disk. The interval needs to be in a format parsable by a [time.Duration](https://pkg.go.dev/time#ParseDuration).
+Note that the interval is not wall-clock time. Rather it is accumulated block processing time after which the state should be flushed.
+For example the value `0s` will essentially turn on archive mode. If set to `1h`, it means that after one hour of effective block processing time, the trie would be flushed. If one block takes 200ms, a flush would occur every `5*3600=18000`  blocks. The default interval for mainnet is `1h`.
+
+Note: this configuration will not be presisted through restarts.
+
+| Client  | Method invocation                                                |
+| :------ | ---------------------------------------------------------------- |
+| Console | `debug.setTrieFlushInterval(interval string)`                    |
+| RPC     | `{"method": "debug_setTrieFlushInterval", "params": [interval]}` |
+
 ### debug_stacks
 
 Returns a printed representation of the stacks of all goroutines.