Request MetaMask network change if the user if on a wrong one

[cs-balazs]

Closes #1

For now on the all communities page, I just hardcoded to request the change to polygon, but I think we should design, and implement a more complex dialog system to let the user know what the chains we support (maybe how many communities are available on them), so the user can choose one.
For this, I think we would have to refactor the community provider, and have an "availableChains" or something like that, which contains the original chainData, not just the "current one". Also, the current chainData key should be undefined if the community is not available on the chosen chain?

I don't really get why we want to show all the communities in the explorer, not just the ones available on the chosen chain, I think we should at least indicate that the community is not available

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