feat(messages): Allow Custom Fields in Messages (#32224)

.changeset/four-eyes-sniff.md

apps/meteor/app/api/server/v1/chat.ts

.../meteor/app/lib/server/functions/processWebhookMessage.ts

apps/meteor/app/lib/server/functions/sendMessage.ts

apps/meteor/app/lib/server/functions/updateMessage.ts

.../meteor/app/lib/server/lib/validateCustomMessageFields.ts

apps/meteor/app/lib/server/methods/updateMessage.ts

apps/meteor/server/settings/message.ts

apps/meteor/tests/end-to-end/api/05-chat.js

...t/app/lib/server/lib/validateCustomMessageFields.tests.ts

packages/core-typings/src/IMessage/IMessage.ts

packages/i18n/src/locales/en.i18n.json

packages/rest-typings/src/v1/chat.ts