Add Search box to Report Source Selection

[davidcui1225]

Issue #, if available:
#264
Description of changes:

• Changed Report source selection in Report settings to be EuiComboBox vs. Drop-down list. Now users can search for their report sources.
• Create report definition no longer has pre-populated report source, users will have to enter it manually
• Added front-end input validation for Report source to verify field is not empty
• Updated cypress test to select report source

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

[codecov]

Codecov Report

Merging #286 (17df648) into dev (45abee7) will increase coverage by 2.33%.
The diff coverage is 93.33%.

@@            Coverage Diff             @@
##              dev     #286      +/-   ##
==========================================
+ Coverage   74.94%   77.27%   +2.33%     
==========================================
  Files          32       32              
  Lines        1764     1769       +5     
  Branches      342      348       +6     
==========================================
+ Hits         1322     1367      +45     
+ Misses        437      397      -40     
  Partials        5        5              

Impacted Files	Coverage Δ
...itions/report_settings/report_settings_helpers.tsx	100.00% <ø> (+6.34%)	⬆️
...rt_definitions/report_settings/report_settings.tsx	89.32% <93.33%> (+14.73%)	⬆️

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[davidcui1225]

codecov failed- will add more tests

[zhongnansu]

Anything else you can do to resolve the codecov failure?

[davidcui1225]

codecov failed- will add more tests

Codecov fixed- coverage raised significantly