[8.16] [Graph] Escape backslash characters in the graph encode functi…

…ons (#196239) (#196683)

# Backport

This will backport the following commits from `main` to `8.16`:
- [[Graph] Escape backslash characters in the graph encode functions
(#196239)](#196239)

<!--- Backport version: 9.4.3 -->

### Questions ?
Please refer to the [Backport tool
documentation](https://github.com/sqren/backport)

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Escape backslash characters in the graph encode functions
(#196239)\n\n## Summary\r\n\r\nEscape backslash characters in the graph
encode
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Escape backslash characters in the graph encode
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Escape backslash characters in the graph encode functions
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encode
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Escape backslash characters in the graph encode functions
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BACKPORT-->

Co-authored-by: Marta Bondyra <[email protected]>

x-pack/plugins/graph/public/helpers/kql_encoder.ts

@@ -10,7 +10,7 @@ import rison from '@kbn/rison';
 import { Workspace } from '../types';
 
 function escapeQuotes(str: string) {
-  return str.replace(/"/g, '\\"');
+  return str.replace(/\\/g, '\\\\').replace(/"/g, '\\"');
 }
 
 export function asKQL(workspace: Workspace, joinBy: 'and' | 'or') {