Stop indexer service in full node OnStop method (#1351)

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## Overview
Closes: #1352

Fixes write to file after node stopped panics that were leading to flaky
failing CI tests.

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## Checklist

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<!-- This is an auto-generated comment: release notes by coderabbit.ai
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## Summary by CodeRabbit

- **Bug Fixes**
- Ensured that the Indexer Service properly stops when the Full Node is
stopped, improving resource management and stability.

- **Documentation**
- Updated the documentation to reflect the change in lifecycle
management of the Indexer Service in relation to the Full Node.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Author: Manav-Aggarwal

node/full.go

@@ -361,6 +361,7 @@ func (n *FullNode) OnStop() {
 	err = multierr.Append(err, n.p2pClient.Close())
 	err = multierr.Append(err, n.hSyncService.Stop())
 	err = multierr.Append(err, n.bSyncService.Stop())
+	err = multierr.Append(err, n.IndexerService.Stop())
 	n.Logger.Error("errors while stopping node:", "errors", err)
 }
 

state/indexer-service.md

@@ -6,7 +6,7 @@ The Indexer service indexes transactions and blocks using events emitted by the
 
 ## Protocol/Component Description
 
-The Indexer service consists of three main components: an event bus, a transaction indexer and a block indexer.
+The Indexer service is started and stopped along with a Full Node. It consists of three main components: an event bus, a transaction indexer and a block indexer.
 
 ### Event Bus