Marketplace: add a route that can open a purchase depending on the ownership id

[cpapazoglou]

In SaaS licensing, customers have the SaaS application from the vendor but the billing is happening in WP.com. In those cases, normally there is a billing section inside that SaaS application. Vendors will need to state that billing is managed by WordPress.com and ideally have a link which redirects to the specific purchase in Calypso.

Currently, we've got a route https://wordpress.com/me/purchases/:domain/:purchaseId that works with purchase_id since we share the ownsership_id with vendors it would make sense also have a https://wordpress.com/me/purchases-by-owner/:ownershipId route.

Related to pedbJv-h-p2#comment-14

[cpapazoglou]

Backlog grooming:

• the page will be the same as the singe purchase page
• we might also create the route and use the same controller that renders the purchase page. It will need though an intermediate function to find the purchase id from the ownnesrhip id (getSitePurchases and filter by ownsershipId, use the purchaseId found and render the /purchases/:purchaseId page

Related function: https://github.com/Automattic/wp-calypso/blob/7655b6d1f326371990851da10ebb97f133fbdc17/client/state/purchases/selectors/get-by-purchase-id.js#L1-L13