Introduce a new ExPlat experiment in 9.2

[pmcpinto]

Description: we want to release a new experiment to monitor the impact of any product changes in WC 9.2. The 9.2 code freeze is on July 24th

Acceptance criteria:

• [ ] Replicate the experiment running in 8.8. In sum, we should expose users who choose one of the following options in the "Add products" task: Physical product, Variable product, Digital product, Grouped product, and External product.
• [ ] Create the experiment P2.
• [ ] Create the experiment in Abacus.
• [ ] Add the segment to the WPCOM core.

[pmcpinto]

cc @louwie17

[louwie17]

Setting this to blocked and awaiting for final confirmation from @SamratBiswas1, as we may focus on the communication clarity before continuing with the auto opt-in for new stores.