Enhancement: Add Links to License Key Activation Docs

### Impacted plugin

Jetpack

### What

During the license activation flow, we don't link to our documentation on activating a license:

- https://jetpack.com/support/activate-a-jetpack-product-via-license-key/#activate-a-license

There are several screens where we could link to the documentation. It might allow customers to solve activation issues on their own.

### How




Start by locating the Jetpack license activation flow corresponding to the three annotated screens and review the linked license-key activation documentation. Add documentation links in the relevant activation screens, then verify that each link opens the intended activation section and does not disrupt the flow.

Written by the indexing model from the issue text.