[MCP] Fixes and Refactoring execute_entity (#2902)

## Why make this change?

### Closes on
- `execute_entity` #2831

## What is this change?
This PR implements built-int tool execute_entity as part of built-in
tools to support execution of stored procedures or functions.

- Performs execute operation on a stored procedure or function entity
- Supports both querying and mutation
- `entity` (required) name and `parameters` (optional based on entity
parameters signature) should be specified (see sample below)
- Operation is performed based on permissions as configured in
dab-config
- Success or Failure message response is generated on execution of the
delete operation

## How was this tested?

- [ ] Manual functional test using MCP inpector/HTTP client
- [ ] Integration Tests
- [ ] Unit Tests

## Sample Request(s)

Execute stored procedure to read queries-

```
POST http://localhost:5000/mcp

{
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "name": "execute_entity",
    "arguments": {
      "entity": "GetBook",
      "parameters": {
        "id": 1
      }
    }
  }
}
```

Execute stored procedure without parameters-

```
POST http://localhost:5000/mcp

{
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "name": "execute_entity",
    "arguments": {
      "entity": "GetBooks"
    }
  }
}
```

---------

Co-authored-by: Copilot <[email protected]>

Author: souvikghosh04