Bug 2069243 - Add the containers component

[bakulf]

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[bendk]

I don't know enough about the containers code to really review this, so I mostly focused on general Rust component issues.

[jonalmeida]

I walked through the code myself locally and it looks fine to me. I don't have a strong sense of what is good rust style these days, but it's good start either way.

We synced on this patch and these are my take-away notes:

• The l10n IDs will be removed in a future iteration because they are desktop only and cannot link to Android.
• A syncable future is separate, but we don't want to combine this component with an existing syncable storage like remote_tabs because it will use a different sync machine for this store.
• Icons and colours need to be generated on the frontend side of the platforms to be used there, and we link them with a shared ID.
• This is an in-memory copy of the containers, and the platforms will push and pull the list from here.