Support jwt in introspection response

It would be nice to provide support for phantom tokens. Many IDPs already have this feature, for example keycloak or curity. The main idea is that when introspect is called, jwt is returned in response. For example, as in keycloak:

{
  "jwt": "eyJhbGciOiJSUzI1NiIsInR5cCIgOiAiSldUIiwia2lkIiA6ICJLb3BHYmVaeFdHSWJ6N2NVbDQzRFNqLXRIS1d5aklpSFB3LTB2bGNpTTJRIn0.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.yiAScO2FDFeRXaYtRBjRuB5Y2pUZVg4dg6J41WL7mKHa3B_Zp1gshGx1W06fQQdFjlAWnz__QiKTqBwznf_ENxmTNP1Cl8e5h3Tv9fnxBWOVrpyCnKiEP1--va8JkFnwuN4x_JXCk_RLasNVK0CK4fm566WaiIstD2JM3-zoM8qzQFipY7EqFwaBZ1SYwIZnZxzKL_F8e6VVk3PnRHJBr0WYWo1uK889DBPZABjxzJlEs5IBeVYATCAwJBqYoPNeB-VPhN9JEFZWjlbBqVDhvw10KRs9JflJPn8IiJGM9zMUl-l5LZrm4pAGG4eC_unwY0ewg9gWI6hgxRNjRzLHMQ"
}

Apparently this is very similar to JWT Response for OAuth Token Introspection

Start by locating Spring Security's OAuth token introspection response handling and compare its behavior with the linked JWT Introspection Response draft. The work is done when introspection responses can include a jwt value for phantom-token use cases, with coverage for the new response behavior.