fortinet_fortigate - use YAML literal for script source (elastic#6379)

All (indented) characters are considered to be content, including white space
characters. This causes the source in the YAML to match the source in the
ingest processor.

https://yaml.org/spec/1.2.2/#812-literal-style

packages/fortinet_fortigate/data_stream/log/elasticsearch/ingest_pipeline/default.yml

@@ -32,7 +32,7 @@ processors:
       if: ctx.syslog5424_sd != null
       description: |
         Splits syslog5424_sd KV list by space and then each by "=" taking into account quoted values.
-      source:
+      source: |
         def splitUnquoted(String input, String sep) {
           def tokens = [];
           def startPosition = 0;