Jetpack Social: Fix upgrade paths

### Impacted plugin

Social

### What

See videos in pdrWKz-YO-p2

A few upgrade paths for Jetpack Social lead to Basic being automatically applied to checkout. We need to redirect customers to Jetpack.com/pricing and open the social modal instead, with Advanced being selected by default ([url here](https://cloud.jetpack.com/pricing#jetpack_social_advanced_yearly)).

This will help with Social Advanced feature discovery & purchase.

### Paths to update:

**Classic editor**
- [ ] "Upgrade" link in sidebar
- [ ] "Learn more link in sidebar

**Social stand-alone**
- [ ] "Get a Jetpack Social Plan" upgrade notice

**Gutenberg Editor**
- [ ] "Upgrade now" link in sidebar
- [ ] "more about Jetpack social" link in sidebar (Redirect works fine. Currently defaults to Basic plan. Change to default to Advanced plan)

Review the five listed upgrade paths across the Classic editor, Social stand-alone, and Gutenberg Editor, using the referenced pricing URL and videos as the behavioral reference. Done means each path redirects to Jetpack.com/pricing, opens the Social modal, and selects Advanced by default rather than Basic.

Written by the indexing model from the issue text.