Implement the offering contracting page v0 (with no backend)

[xamcost]

Hi there! The goal of this issue is to add a page in the UI to contract an offering. This page corresponds to the one being displayed when a user selects an offering amongst the results of a search in the catalogue. At this stage, we just want to lay the page structure, following the mock-up of the v0 accessible here, and shown here for convenience:

Since no API is yet available to fetch data about participants or offerings, all info on these page should be mocked.