Design Picker: Integrate Blank Canvas custom item in the grid of designs

[razvanpapadopol]

What

We want to add an internal prototype flow for a Blank Canvas option in /new.

Why

We want the user to have the opportunity to start a site without any design (i.e. a blank canvas).

A/C

• [x] The theme has an empty thumbnail (see the example from Themes showcase: https://cloudup.com/cTv4ZJchXoZ) and this https://github.com/Automattic/wp-calypso/issues/49141#issuecomment-773700429.
• [x] The theme is always the first in the list (i.e. excluded from randomization). We could use the slug (blank-canvas) to differentiate.
• [x] The theme's name is Start with an empty page and is marked for translations (thus ignoring the value from the JSON configuration) (see this comment for more context)
• [x] The <DesignPicker/> works with the blank canvas enabled or disabled (use the is-alpha flag to differ).
• [x] Unit tests are written and pass for the blank canvas edge case.

Additional info

Original issue: https://github.com/Automattic/wp-calypso/issues/49141

Blocked by: #51979

[simison]

The theme has an empty thumbnail (see the example from Themes showcase: https://cloudup.com/cTv4ZJchXoZ) and this #49141 (comment).

Latest design; p9Jlb4-2qt-p2 — those other ones you linked were older:

[razvanpapadopol]

@kwight, we assume that Blank Canvas template is not going to be an option for the AnchorFM flavored onboarding. Is this correct?

[kwight]

@razvanpapadopol Correct, Anchor flows have their own template automatically assigned.