Built-in plugin and external ones: what should we include by default in the main app?

During the AiiDAlab GM, we pointed out that we should decide on what plugins we include in the main QeApp (this one) by default: for examples the bands, pdos, xps plugins/functionalities are delivered in the main source code (i.e. no need to download and install them from the [plugin list](https://github.com/aiidalab/aiidalab-qe/blob/main/plugin_list.ipynb) page).

Instead, the [muon app](https://github.com/mikibonacci/aiidalab-qe-muon) and the [vibro app - phonons](https://github.com/mikibonacci/aiidalab-qe-vibroscopy) plugins need to be downloaded afterwards.

We are thinking on the possibility to include some of this (still) external plugins in the core QeApp.
I am not a fan of this, as it will then require to install several additional packages (aiida-muon, aiida-impuritysupercellconv, aiida-vibroscopy, aiida-phonopy, phonopy and so on), but I see the point of having already additional core functionalities available with just the main installation. I am not sure if the muons are a core functionalities, but the phonons probably are.

Moreover, what about the time to perfomance on container startup, in case we pre-install the QeApp, and so all the built-in plugins? @unkcpz

Another idea could be to put a sentence/button in panel 2, where the list of available properties is presented, redirecting to the plugin list page to inspect and install more plugins (features) if required.

Pinning @giovannipizzi and @unkcpz for more comments on that.