Importers: Consolidate list of supported/available importers

[daledupreez]

Details

We have multiple places in Calypso that track permitted/enabled importers, including the following:

• getConfig() and getImporters() in client/lib/importer/importer-config.tsx
• The logic in getFinalImporterUrl() in client/landing/stepper/declarative-flow/internals/steps-repository/import/helper.ts includes a local productImporters constant
• The ListStep component in client/blocks/import/list/index.tsx includes a hard-coded list of primary and secondary import platforms

Checklist

• Confirm which platforms should be enabled during import flows
• Confirm which location we're going to use as our source of truth
• Update callers to use the primary location

Related

No response

[markbiek]

To help wrap my head around this a bit, I've created a spreadsheet of the different engines and locations in Calypso:

34b20-pb/#bash

It makes the most sense to me to consolidate everything into getConfig in lib/importer/importer-config.tsx. The other functions are using a subset of the data defined in getConfig so it seems reasonable that they can pull their data from getConfig instead.

We can also add a primary/secondary designation that the ListStep could use.

[markbiek]

Confirm which platforms should be enabled during import flows

@daledupreez The one thing I'm not sure about is how to confirm the above.

[markbiek]

Also noting that we may want to move the ImporterPlatform and relates types out of client/blocks/import/types.ts and into importer-config.tsx.

[markbiek]

Leaving this open as I'm going to move some of the importer-related types around in a separate PR.