Log4j JsonTemplateLayout w/ local decorating - Properly support escaped double quotes followed by a comma

[jtduffy]

Description

An edge case was discovered where malformed JSON was generated using the JsonTemplateLayout instrumentation module with a log message that contained an escaped double quote followed by a comma.

For example, this log line:
LOGGER.info("info {}", "\"bar\",");

produces the following JSON (prior to local decorating):

{
  "instant" : {
    "epochSecond" : 1734983121,
    "nanoOfSecond" : 537701000
  },
  "thread" : "background-preinit",
  "level" : "INFO",
  "loggerName" : "org.hibernate.validator.internal.util.Version",
  "message" : "info \"bar\",",
  "endOfBatch" : true,
  "loggerFqcn" : "org.hibernate.validator.internal.util.logging.Log_$logger",
  "threadId" : 75,
  "threadPriority" : 5
}

which is valid JSON.

With local decorating enabled, the instrumentation module injects the NR-LINKING metadata as follows:

{
  "instant" : {
    "epochSecond" : 1734983121,
    "nanoOfSecond" : 537701000
  },
  "thread" : "background-preinit",
  "level" : "INFO",
  "loggerName" : "org.hibernate.validator.internal.util.Version",
  "message" : "info \"bar\ NR-LINKING|abc12345|7253f5d752ed8f11|async-logger-tests|",",
  "endOfBatch" : true,
  "loggerFqcn" : "org.hibernate.validator.internal.util.logging.Log_$logger",
  "threadId" : 75,
  "threadPriority" : 5
}

which is invalid JSON since we inject in between the escaped \ and ",

The code currently checks for ", in order to get the index for metadata injection.
https://github.com/newrelic/newrelic-java-agent/blob/3cd9554e59a6575522a862178f78e6ef022a5a17/instrumentation/apache-log4j-layout-template-json-2.14.0/src/main/java/com/nr/agent/instrumentation/log4j2/layout/template/json/AgentUtils.java

We need to check for an unescaped " followed by a , and adjust the metadata addition appropriately.

[workato-integration]

https://new-relic.atlassian.net/browse/NR-353411