feat: support chat relay in frontend

[DorraJaouad]

☑️ Resolves

• Part of ⏩ Chat relay via High-performance backend #624
• To test and while you don't have the latest master from signaling, overwrite its feature like:

this.features['chat-relay'] = true // TEMPORARY Always supported by standalone signaling server.

in Signaling.Standalone.prototype.helloResponseReceived

🏁 Checklist

• 🌏 Tested with different browsers / clients:
  • Chromium (Chrome / Edge / Opera / Brave)
  • Firefox
  • Safari
  • Talk Desktop
  • Integrations with Files sidebar and other apps
  • Not risky to browser differences / client
• 🖌️ Design was reviewed, approved or inspired by the design team
• ⛑️ Tests are included or not possible
• 📗 User documentation in https://github.com/nextcloud/documentation/tree/master/user_manual/talk has been updated or is not required

[Antreesy]

Before I forget: since we decided to go with experimental flag, please wrap the code handling with it =)
It doesn't require any changes on backend for proper testing

const experimentalChatRelay = (getTalkConfig('local', 'experiments', 'enabled') ?? 0) & CONFIG.EXPERIMENTAL.CHAT_RELAY

export const CONFIG = {
	EXPERIMENTAL: {
		/**
		 * Since 22.0.3 ??
		 * Some description to align with Anna's PR
		 */
		CHAT_RELAY: 4,
	},
} as const

[Antreesy]

Otherwise seems good to be merged

[Antreesy]

/backport to stable32