Implement build checks UI

[apburnes]

User stories:

• As a developer or product owner responsible for ensuring that my agency's Pages site is secure and usable, I want to see if my code and site have any obvious security or usability problems.
• As a developer responsible for addressing security or accessibility issues for a Pages site, I want to know precisely where any discovered issues are, and see documentation or remediation steps for each issue.
• As a developer adding new features, or a content manager adding new content, I want to make sure that I am not introducing new security or usability/accessibility problems when I contribute to my Pages site, even on non-production branches.
• As a compliance analyst or site manager responsible for ensuring that my agency's technology products fulfill 21st Century IDEA, ATO, and SSP requirements, I want to directly access and keep records of my site's required scans.

Tasks

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1. scans for each build https://pages.cloud.gov/sites/<site-id>/builds/<build-id>/scans
2. scan button on each build log https://pages.cloud.gov/sites/<site-id>/builds/<build-id>/logs
3. builds history https://pages.cloud.gov/sites/<site-id>/builds
4. DEFERRED: site settings https://pages.cloud.gov/sites/<site-id>/settings (TBD)
5. DEFERRED: scans history https://pages.cloud.gov/sites/<site-id>/scans

[sknep]

We're holding off on Site Settings and Scan History page for now, right? Open to hearing otherwise.

[sknep]

@drewbo should writing docs and customer comms happen as part of this ticket or do we want to do those later/on another ticket?

[drewbo]

let's have those as later tickets since we can't go to production without the SCR first (the UI being built will happen prior to everything else)