Upgrade snakeyaml dependency.

[mashhurs]

What does this PR change?

Upgrades snakeyaml to 2.0.

How to test locally?

• build jar with ./gradlew clean vendor
  • creates logstash-filter-useragent-3.3.5.jar
• define a config to use the plugin

input {
  stdin {}
}
filter {
  useragent {
    source => 'message'
  }
}
output {
 stdout {}
}

• run Logstash and check if plugin is parsing the user agent info

Mozilla/5.0 (iPad; U; CPU OS 3_2_1 like Mac OS X; en-us) AppleWebKit/531.21.10 (KHTML, like Gecko) Mobile/7B405
{
          "host" => {
        "hostname" => "Mashhurs-MacBook-Pro.local"
    },
      "@version" => "1",
    "@timestamp" => 2023-09-19T03:44:35.218216Z,
    "user_agent" => {
            "os" => {
               "full" => "iOS 3.2.1",
            "version" => "3.2.1",
               "name" => "iOS"
        },
          "name" => "Mobile Safari UI/WKWebView",
        "device" => {
            "name" => "iPad"
        }
    },
       "message" => "Mozilla/5.0 (iPad; U; CPU OS 3_2_1 like Mac OS X; en-us) AppleWebKit/531.21.10 (KHTML, like Gecko) Mobile/7B405",
         "event" => {
        "original" => "Mozilla/5.0 (iPad; U; CPU OS 3_2_1 like Mac OS X; en-us) AppleWebKit/531.21.10 (KHTML, like Gecko) Mobile/7B405"
    }
}

• Closes Upgrade snakeyaml dependency. #88

[andsel]

Left a doubt on the fact to restrict LS version compatibility.

[andsel]

Snakeyaml was updated on Logstash core with elastic/logstash#15125, shipped with v8.9.0. Should we constraint this version of the plugin to that LS versions ? (add a dependency on LS 8.9.0+ in gemspec)

[mashhurs]

With this change, we see with the CIs that it is compatible with the current latest 8.x and 7.x version. We should investigate the case where LS core has a lower version than plugin but for now, pessimistic locking without clarification would block some users after release.

[andsel]

LGTM