🚀 Feature: Add Variable Support in Messaging Subject and Body

### 🔖 Feature description Coming from the discord suggestion here - https://discord.com/channels/564160730845151244/564160731327758347/1211961183897124884 Currently, the Messaging interface scheduled for `1.5`, as demonstrated in the showcase on Youtube by Dennis, lacks the ability to dynamically insert user or project-specific details into message subject or content. --- The current messaging interface is depicted here (screenshot from the product showcase): <img src="https://cdn.discordapp.com/attachments/564160731327758347/1211961182940958750/Appwrite_Compose_A_Message.png?ex=65f019cf&is=65dda4cf&hm=5e25c348de611f16e8fd6322be423f4b3c2127e8263e69e2b909833b8bfaed6f&"> I suggest adding the use of variables within the subject and body of messages. These variables would then map to actual data such as the recipient's name, project name, or any other relevant information that can be dynamically inserted into messages. --- The proposed change is similar to what Auth Email Template supports like below - <img src="https://cdn.discordapp.com/attachments/564160731327758347/1211961183641538570/Message_Variables.png?ex=65f019cf&is=65dda4cf&hm=55c5c1f819a781c6dfd5383c2dfc4012ddf87e8205ac85bb7c34cbbaf16a385d&" /> ### 🎤 Pitch The Messages would feel more direct, targeted and personal to the recipients. Example: > Hello Appwriters, > We hope you all are doing well! > > This week, we're thrilled to announce the launch of Appwrite Messaging, a dynamic way to connect with your users via Emails, SMS, & Push Notifications effortlessly! > > Embrace this game-changing feature by integrating it into your projects today. VS > Hi Darshan, > We hope you're doing well! > > Exciting news - **Appwrite Messaging** has just landed! > **Appwrite Messaging** enables seamless connection with your audience through Emails, SMS, & Push Notifications. > > Why not give it a spin with your 'Blaze' Project? > It's the perfect opportunity to transform how you engage with your users. Let's make your …