Create Safe6900 Module

[akshay-ap]

ERC-6900 is a standard for modular accounts which is compatible with ERC4337.

This issue aims at creating a ERC-6900 compatible version of Safe via a module.

The code of the implementation can be tracked in the branch here:
https://github.com/safe-global/safe-modules/tree/feature-safe-module-6900

To do:

• Create interfaces for plugins
• Add validation for transaction execution
• Add code for installing plugin
• Add code for uninstalling plugin
• Create sample plugin
• Documentation

Additional reocurces:

• https://www.erc6900.io/