A pipeline can pause and ask for user input at any point.

This needs to be exposed via the blue ocean REST api - both that it is waiting, but also that it can take a POST of data to acknowledge it. The input may take the form of Yes/No or it may be a richer set of input.

In Scope:

• API to fetch any pipelines blocked on "input" (for current user)
• API to fetch what input is required from user (so a form can be built up on the client)
• API to post confirmation from user (binary yes/no)
• API to take a post of data from user (for non yes/no)
  (these are not necessarily separate unrelated apis, just that there needs to be support for those types of features)

Out of scope:
(perhaps we should start with simple yes/no)