[BIZ-1943] Refactor sales section, add overview and example proposal.
This MR breaks the sales process page down into several subpages. It also adds an overview section to sales that summarizes the customer lifecycle and adds an example proposal PDF so that developers can see what the client sees when the proposal/discovery process is completed.
JIRA tickets: https://tasks.opencraft.com/browse/BIZ-1943
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