1:many, many:1 relationships for Vulnerabilities
### Description
The initial iteration of first class vulnerabilities has a linear path from vulnerability occurrence in a branch to vulnerability in the default branch to Issue. These 1:1 relationships are useful for tracking and remediating vulnerabilities but provide for only the most basic of workflow scenarios. We need to expand to include 1:many and many:1 use cases.
We need to explore the following use cases:
1. multiple vulnerability occurrences linked to a single existing vulnerability object
1. multiple vulnerability objects linked to the same Issue
1. one vulnerability object linked to multiple Issues
### Theme
* Cover a broad set of use cases in vulnerability tracking and remediation workflows
### Objectives
* Verify or reject validity of above use cases
* Identify any missing valid use cases
* Create UX designs to support workflows for each valid use case
* Create UX designs to account for changes to Security Dashboards
* Update underlying data models to accommodate identified valid use cases
### Value delivered
* Vulnerability management will be more efficient due to less redundant or duplicated occurrences and remediation Issues.
* Users will have more flexibility in how they manage and track vulnerabilities.
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