fix(app): Center app and robot update modals

[mjhuff]

Closes RQA-2349

Overview

This PR fixes an issue in which the app and robot update modals are not properly centered (as a bonus, the module setup modal is also properly centered).

There's a lot we can do to make this issue less likely to occur in the future, and I've added a note to revisit this topic in the tech debt paydown doc. Because we don't have standardized modal sizing, custom modal widths require a custom left margin offset in order to be properly centered.

At a bare minimum, adding testing to custom width/left-margin modals is a good idea. This at least shows we've gone out of the way to center the modal properly, and anyone who tries to adjust width only will fail a test and have to re-center the modal.

A better, longer-term solution off the top of my head would be to standardize modal sizes (convo w/ design).

Test Plan

• Downloaded this build of the app.
• Verified that the app update modal is centered (select the alpha channel if you aren't already on it).
• Opened up a robot update modal and verify the robot update modal is centered.
• Verified that no other modals were negatively impacted by this change.
• If you'd like to try this yourself and you don't have a robot, you may have to finagle the code a bit to get the banners to show, but it is possible!

Changelog

• Desktop app update modals are now properly centered.

Risk assessment

low

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (78c85fc) 67.74% compared to head (bd5a042) 67.74%.
Report is 2 commits behind head on chore_release-7.2.0.

Additional details and impacted files

@@                   Coverage Diff                   @@
##           chore_release-7.2.0   #14541      +/-   ##
=======================================================
- Coverage                67.74%   67.74%   -0.01%     
=======================================================
  Files                     2517     2517              
  Lines                    72087    72150      +63     
  Branches                  9284     9330      +46     
=======================================================
+ Hits                     48834    48876      +42     
- Misses                   21035    21051      +16     
- Partials                  2218     2223       +5     

Flag	Coverage Δ
app	64.64% <100.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
app/src/molecules/LegacyModal/index.tsx	100.00% <100.00%> (ø)
...RobotSettings/UpdateBuildroot/UpdateRobotModal.tsx	81.25% <ø> (ø)
...RobotSettingsDashboard/RobotSystemVersionModal.tsx	100.00% <ø> (ø)
app/src/organisms/UpdateAppModal/index.tsx	89.47% <ø> (ø)

... and 4 files with indirect coverage changes

[koji]

LGTM!