feat: create 'GuildTemplate' & add 'Client#fetchGuildTemplate()'

[izexi]

• Ref: Document Server Templates discord/discord-api-docs#1712
• Adds DataResolver#resolveGuildTemplateCode() to resolve template URLs
• Along with DataResolver#resolveCode() to reuse code for the above and the resolveInviteCode method
• Creates a GuildTemplate structure with a createGuild method to add support for the POST /guilds/templates/:template_code endpoint
• Adds Client#fetchGuildTemplate() to support for the GET /guilds/templates/:template_code endpoint
• Resolves Idea: Server templates #4651

Here's a snippet of how I tested these changes

import { once } from 'events';
import { Client, DataResolver, GuildTemplate } from 'discord.js';
import { TEST_TEMPLATE_CODE, TOKEN } from './constants';

const client = new Client();
let createdGuild;

client.login(TOKEN);

test('DataResolver#resolveGuildTemplateCode()', () => {
  expect(
    DataResolver.resolveGuildTemplateCode(
      'https://discord.com/template/FKvmczH2HyUf'
    )
  ).toBe('FKvmczH2HyUf');

  expect(
    DataResolver.resolveGuildTemplateCode('https://discord.new/FKvmczH2HyUf')
  ).toBe('FKvmczH2HyUf');

  expect(
    DataResolver.resolveGuildTemplateCode('https://discord.invalid/code')
  ).toBe('https://discord.invalid/code');
});


test('Client#fetchGuildTemplate() & GuildTempalte#createGuild()', async () => {
  await once(client, 'ready');

  const template = await client.fetchGuildTemplate(TEST_TEMPLATE_CODE);
  expect(template).toBeInstanceOf(GuildTemplate);

  const createdGuildName = 'foo';
  createdGuild = await template.createGuild(createdGuildName);
  expect(createdGuild.name).toBe(createdGuildName);
});

afterAll(() => createdGuild.delete());

Status

• Code changes have been tested against the Discord API, or there are no code changes
• I know how to update typings and have done so, or typings don't need updating

Semantic versioning classification:

• This PR changes the library's interface (methods or parameters added)
  • This PR includes breaking changes (methods removed or renamed, parameters moved or removed)
• This PR only includes non-code changes, like changes to documentation, README, etc.

[NotSugden]

json error code 10057 unknown guild template could be added to this PR https://discord.com/developers/docs/topics/opcodes-and-status-codes#json

[izexi]

Closing this PR since its being superseded by #4907 and the referenced API docs PR on there has been merged