Add Support for QWATCH Command with HTTP

[pratikpandey21]

Description

Implement support for the QWATCH command over HTTP, utilizing Server-Sent Events (SSE) to enable real-time updates to clients based on changes to underlying data. This enhancement will allow HTTP clients to subscribe to SQL-like queries over data structures and receive push notifications whenever the results of the query change, providing a more efficient alternative to polling for updates.

Command Overview:

Command: QWATCH
HTTP Method: POST
Endpoint: /QWATCH
Body: SQL Query. Check here for Query reference.

Behaviour with HTTP:

Subscription Mechanism:

• When an HTTP client sends a POST request to the /QWATCH endpoint with the query parameter, the server establishes a persistent connection using Server-Sent Events (SSE).
• The server continuously monitors the data matching the specified query.
• Whenever a data modification affects the query results, the server updates the client over the SSE connection.

Response Format:

The server responds with an HTTP 200 OK status and sets the Content-Type header to text/event-stream.
Each update is sent as an SSE event with the following format:

data: [{"key": "<key>", "value": <JSON value>}]

Tasks:

• Implement the /QWATCH endpoint to accept HTTP POST requests.
• Establish an SSE connection and manage it efficiently to support multiple concurrent clients.
• Create comprehensive documentation for using QWATCH over HTTP, including examples.

[lucifercr07]

@pratikpandey21 would like to work on this.

[lucifercr07]

Closing, merged as part of #614