fix(dashboards): Accommodate larger screens on dashboards overview

[nikkikapadia]

Allows for more than three cards in a row on the dashboards overview on larger screens. Also allows for as many dashboards needed to fill the page to be previewed instead of 9.

before:

after:

[codecov]

Codecov Report

Attention: Patch coverage is 72.72727% with 6 lines in your changes missing coverage. Please review.

✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
static/app/views/dashboards/manage/index.tsx	72.72%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #78719      +/-   ##
==========================================
+ Coverage   78.21%   78.24%   +0.02%     
==========================================
  Files        7104     7107       +3     
  Lines      312956   313078     +122     
  Branches    51106    51109       +3     
==========================================
+ Hits       244790   244958     +168     
+ Misses      61805    61760      -45     
+ Partials     6361     6360       -1