Add plugins to uiConfig

[conduongtong]

Prerequisites

• I have written a descriptive issue title
• I have searched existing issues to ensure the issue has not already been raised

Issue

I want to add a custom plugins filter by tag with case insensitive like this post:
swagger-api/swagger-ui#3876 (comment)

I try to add but it's not working.

fastify.register(fastifySwaggerUI, {
      routePrefix: '/documentation',
      uiConfig: {
        displayRequestDuration: true,
        filter: true,
        tryItOutEnabled: true,
        plugins: [CaseInsensitiveFilterPlugin],
      },
    });

const CaseInsensitiveFilterPlugin = function (system) {
  return {
    fn: {
      opsFilter: (taggedOps, phrase) => {
        console.log('test');
        return taggedOps.filter((tagObj, tag) => tag.toLowerCase().indexOf(phrase.toLowerCase()) !== -1);
      },
    },
  };
};

[Uzlopak]

Basically the duplicate of #25 .

The issue is that the uiConfig is serialized to json and supplied by a rest-call. And functions cant be serialized. I will close this in favor of #25