Pending job sync

[elioschmutz]

This PR introduces the @update-pending-signing-job endpoint and provides the update_url to the sign service which will use it to sync editors and signers from skribble to gever.

See related ogsign-PR: https://github.com/4teamwork/ogsign/pull/13 for the implementation there.

The PR adressses the PATCH /<update_url> section of this chart:

┌───────┐                          ┌────────┐                    ┌───────────┐
│       │ POST /signing-jobs/      │        │                    │           │
│       ├─────────────────────────►│        │                    │           │
│       │                          │        │ POST /convert      │           │
│       │                          │        ├───────────────────►│           │
│       │                          │        │◄-------------------│           │
│       │                          │        │                    │           │
│       │                          │        │                    │ Bumblebee │
│       │                          │        │ POST /bb-callback  │           │
│       │                          │        │◄───────────────────┤           │
│       │                          │        │-------------------►│           │
│       │                          │        │                    │           │
│       │                          │        │                    │           │
│       │                          │        │                    │           │
│       │                          │        │                    └───────────┘
│       │                          │        │
│ GEVER │                          │ ogsign │                    ┌───────────┐
│       │                          │        │(start signing req) │           │
│       │                          │        ├───────────────────►│           │
│       │                          │        │◄-------------------│           │
│       │   {"redirect_url": ...}  │        │                    │           │
│       │◄-------------------------│        │                    │           │
│       │                          │        │                    │  External │
│       │                          │        │       (poll)       │           │
│       │                          │        ├───────────────────►│  Signing  │
│       │                          │        │                    │           │
│       │                          │        │                    │  Provider │
│       │                          │        │                    │           │
│       │ PATCH /<update_url>      │        │   (state changed)  │           │
│       │◄─────────────────────────│        │◄-------------------│           │
│       │                          │        │                    │           │
│       │ POST /<upload_url>       │        │     (signed PDF)   │           │
│       │◄─────────────────────────┤        │◄-------------------│           │
│       │-------------------------►┤        │                    │           │
└───────┘                          └────────┘                    └───────────┘

For TI-1494

Checklist

Everything has to be done/checked. Checked but not present means the author deemed it unnecessary.

• Changelog entry
• Link to issue (Jira or GitHub) and backlink in issue (Jira)

[buchi]

👍🏻 LGTM

[buchi]

Suggested change

	Provides an endpoint to sync pending signing jobs with the external sign service. [elioschmutz]
	Provide an endpoint to sync pending signing jobs with the external sign service. [elioschmutz]