Add event handlers

You can find the list of event handlers emitted by the lens contract [here](https://docs.lens.xyz/docs/events). As of now, only one event handler is done, all others have remained. Following is the list of event handlers that need to be added for a usable MVP.

- [x] #14
- [x] #15
- [x] #16
- [x] #17
- [ ] #18
- [ ] #19

Feel free to suggest an addition/deletion of any event handler. Steps to add an eventHandler:
1. Define a function to handle any event in the `src/lens-hub.ts` file in our project as it is defined [here](https://github.com/Developer-DAO/Lens-Graph-Subgraph/blob/841a59861bb3b9d577fe1882a32b1373dd9e7819/src/lens-hub.ts#L40). You can get the details about the event fields from the [lens-docs](https://docs.lens.xyz/docs/lenshub). Also, you can use this tool called [tenderly](https://dashboard.tenderly.co/explorer) if you have an address of that particular transaction and this tool will provide you with all the information regarding the events emitted.
2. Once the event handler is defined in the `lens-hub.ts` file, add that event handler in the `subgraph.yml` file as shown [here](https://github.com/Developer-DAO/Lens-Graph-Subgraph/blob/841a59861bb3b9d577fe1882a32b1373dd9e7819/subgraph.yaml#L59)