Add snaps API for adding tab to transaction approval

[danfinlay]

We have had a recurring idea from a couple possible snaps developing teams. The type of teams include:

• Contract security auditors
• Smart contract analyzers
• Smart contract decompilers
• Metadata decoders
• Gas price analyzers

These use cases would like to add an extra tab to the transaction confirmation screen (currently Details and Data). This would allow services to add an extra layer of analysis to the view a person sees before a final confirmation.

Opening the topic here for further discussion.

[crazyrabbitLTC]

Yes, it would be nice if we could have a part of the MetaMask UI to use to communicate information via the plugin. Plugins are great, but in terms of the idea of having a security auditor plugin, it would be good to be able to have some space to see data about what is being shown.

Also, the metamask UI might be a good location for plugings that have some sort of minimum settings required- for example login for decentralized storage, or something like that.

[crazyrabbitLTC]

I imagine this box could be identified by some sort of marker from Metamask saying something like, "This is a plugin, not Metamask" just to be clear.

[danfinlay]

To drill more carefully on the problem of labeling plugins within our UI, I've opened this issue: #115