[e2e] Document issues with Percy

[unlikelyzero]

Summary

As we're nearing another release, we need to document some of the known issues with Percy so that folks know what to ignore.

• Icons do not load randomly.

I believe the answer lies in the percy debug statements

[percy:core:discovery] Handling request: http://localhost:8080/ (2ms)
[percy:core:discovery] - Serving root resource (0ms)
[percy:core:discovery] Handling request: http://localhost:8080/dist/espressoTheme.css (15ms)
[percy:core:discovery] - Resource cache hit (0ms)
[percy:core:page] Page navigated (65ms)
[percy:core:discovery] Wait for 100ms idle (0ms)
[percy:core:discovery] Handling request: http://localhost:8080/dist/images/logo-openmct.svg (38ms)
[percy:core:discovery] - Resource cache hit (0ms)
[percy:core:discovery] Handling request: http://localhost:8080/dist/fonts/Open-MCT-Symbols-16px.woff (1ms)
[percy:core:discovery] - Resource cache hit (0ms)

The above shows that the fonts are loaded separately from the rendered dom in playwright. The fix would be to add some sort of time delay to the snapshot.

• Header values shift slightly.

This is likely due to https://github.com//issues/6819

• SWG are not clock controlled https://percy.io/b2e34b17/openmct/builds/36572612/changed/1998390497?browser=chrome&browser_ids=59&group_snapshots_by=similar_diff&subcategories=unreviewed%2Cchanges_requested&utm_source=github_status_public&viewLayout=overlay&viewMode=new&width=1024&widths=1024