Add UI components that allows feature owners to supply a continuity ID for security review

[DanielRyanSmith]

This is part of the work for integrating ChromeStatus with IssueTracker API in order to create and reference security review bugs. Feature owners should be able to supply a existing continuity ID when requesting a security review.

A new “Continuity ID” feature-level field will exist in ChromeStatus (with one ID associated at maximum with each feature). When the feature owner selects “Request Review” or “Request N/A” in ChromeStatus for the “WP Security” gate in an origin trial or shipping stage, a new modal will appear asking the user to optionally provide a continuity ID if it exists, along with a detailed description of which bug represents the continuity bug.

• A new dialog should be displayed to the user, similar to chromedash-add-stage-dialog.ts.
• If the user provides a continuity ID, ChromeStatus will run a query against other existing features to determine if the given continuity ID is already in use.
• The continuity ID will be rejected if it is found to be associated with another feature.
• The user should be able to NOT provide a continuity ID, which will trigger bug creation without the continuity ID.