Add policy_auto_dismissed field to Vulnerabilities ES index

What does this MR do and why?

This MR adds the policy_auto_dismissed field to Vulnerabilities ES index.

References

Related to: #581391

Screenshots or screen recordings

How to set up and validate locally

1. Follow the ES installation instructions first.

   Enable and set up Elasticsearch: https://gitlab.com/gitlab-org/gitlab-development-kit/-/blob/main/doc/howto/elasticsearch.md?ref_type=heads

2. Verify that the Elasticsearch mapping includes the policy_auto_dismissed field

   Run the following command in your terminal to check the field mapping for vulnerabilities in Elasticsearch:

   curl -s "http://localhost:9200/gitlab-development-vulnerabilities-*/_mapping?pretty" | grep -A5 policy_auto_dismissed

   Expected output:

      "policy_auto_dismissed" : {
          "type" : "boolean"
        },
   

This confirms that the policy_auto_dismissed field is correctly indexed and available for use in vulnerability documents.

MR acceptance checklist

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