[frontend] Spacing is not correct in dissemination list table between search and headers (#9880)

[SarahBocognano]

Proposed changes

• Making the "gap" styling in PageContainer facultative to avoid the gap between search and list
• Adding a MarginBottom to the AlertInfo Component

Related issues

• Spacing is not correct in dissemination list table between search and headers #9880

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 64.28%. Comparing base (7d55b76) to head (26b8f05).
Report is 3 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #9911      +/-   ##
==========================================
- Coverage   64.29%   64.28%   -0.01%     
==========================================
  Files         655      655              
  Lines       62933    62933              
  Branches     6964     6961       -3     
==========================================
- Hits        40460    40458       -2     
- Misses      22473    22475       +2     

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