Add parse XML docs

_data-prepper/pipelines/configuration/processors/parse-xml.md

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+---
+layout: default
+title: parse_xml
+parent: Processors
+grand_parent: Pipelines
+nav_order: 83
+---
+
+# parse_xml
+
+The `parse_xml` processor parses XML data for an event.
+
+## Configuration
+
+You can configure the `parse_xml` processor with the following options.
+
+| Option | Required | Type | Description |
+| :--- | :--- | :--- | :--- | 
+| `source` | No | String | The field in the `event` object that is parsed. Default value is `message`. |
+| `destination` | No | String | The destination field of the parsed XML. Defaults to the root of the `event`. Cannot be `""`, `/`, or any white-space-only string because these are not valid `event` fields. |
+| `pointer` | No | String | A JSON pointer to the field to be parsed. The value is null by default, meaning that the entire `source` is parsed. The `pointer` can access JSON array indexes as well. If the JSON pointer is invalid, then the entire `source` data is parsed into the outgoing `event` object. If the key that is pointed to already exists in the `event` object and the `destination` is the root, then the pointer uses the entire path of the key. |
+| `parse_when` | No | String | Specifies under what conditions the processor should perform parsing. Default is no condition. Accepts a Data Prepper expression string following the [Data Prepper Expression Syntax]({{site.url}}{{site.baseurl}}/data-prepper/pipelines/expression-syntax/). |
+| `tags_on_failure` | No | String | A list of strings that specify the tags to be set if the processor fails or an unknown exception occurs while parsing. 
+
+## Usage
+
+The following examples show how to use the `parse_xml` processor in your pipeline.
+
+### Example: Minimum configuration
+
+The following example shows the minimum configuration for the `parse_xml` processor:
+
+```yaml
+parse-xml-pipeline:
+  source:
+    stdin:
+  processor:
+    - parse_xml:
+        source: "my_xml"
+  sink:
+    - stdout:
+```
+{% include copy.html %}
+
+When the input event contains the following data:
+
+```
+{ "my_xml": "<Person><name>John Doe</name><age>30</age></Person>" }
+```
+
+The processor parses the event into the following output:
+
+```
+{ "name": "John Doe", "age": "30" }
+```