feat: support frontend plugins via env.config.jsx

[arbrandes]

This provides a mechanism to configure frontend plugins using patches to a base env.config.jsx, in such a way that multiple plugins can take advantage of the file (including for purposes beyond frontend plugins) without clobbering each other.

This is an alternate approach to #233.

[arbrandes]

@hinakhadim, I'm particularly interested in your take on whether the provided patches are sufficient for Indigo.

[hinakhadim]

This is an excellent approach! It enables plugin developers to make adjustments to env.config.jsx indirectly, preserving the original file. In essence, it should function well even when multiple plugins are involved and will work well for indigo. The documentation is very well done, outstanding work!

• If possible, could we include an example of this approach in the documentation for better understanding?
• One consideration: as the list of plugin_slots grows, it might lead to a large number of patches. I’m not entirely sure about the implications of this. In other words, we have to manage the list of plugin_slots. If a plugin_slot name changes, then we have to update it here too. I am assuming it is based on the point 3 in this conversation. I’ll test this out and will be happy to share feedback based on testing with tutor-indigo.