CIF-1535 - Support placeholder text in searchbar component

[herzog31]

Description

• Added placeholder to searchbar component. The placeholder can be changed by defining the placeholder property.
• Updated component readme.
• Added placeholder property to CIF component library as example.

How Has This Been Tested?

• Manually tested

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• I have signed the Adobe Open Source CLA.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes and the overall coverage did not decrease.
• All unit tests pass on CircleCi.
• I ran all tests locally and they pass.

[codecov]

Codecov Report

Merging #371 into master will decrease coverage by 10.71%.
The diff coverage is n/a.

@@              Coverage Diff              @@
##             master     #371       +/-   ##
=============================================
- Coverage     84.50%   73.79%   -10.72%     
+ Complexity      855      631      -224     
=============================================
  Files           174      174               
  Lines          4388     4388               
  Branches        590      588        -2     
=============================================
- Hits           3708     3238      -470     
- Misses          553      954      +401     
- Partials        127      196       +69     

Flag	Coverage Δ	Complexity Δ
#integration	67.10% <ø> (ø)	631.00 <ø> (ø)
#jest	77.36% <ø> (ø)	0.00 <ø> (ø)
#karma	93.93% <ø> (ø)	0.00 <ø> (ø)
#unittests	?	?

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

Impacted Files	Coverage Δ	Complexity Δ
...s/internal/servlets/SpecificPageFilterFactory.java	0.00% <0.00%> (-90.91%)	0.00% <0.00%> (-6.00%)
...e/components/internal/servlets/PreviewServlet.java	6.66% <0.00%> (-90.00%)	2.00% <0.00%> (-6.00%)
...elatedproducts/RelationTypesDataSourceServlet.java	7.14% <0.00%> (-85.72%)	1.00% <0.00%> (-3.00%)
...ernal/servlets/GraphqlClientDataSourceServlet.java	15.38% <0.00%> (-74.36%)	3.00% <0.00%> (-4.00%)
...commerce/core/components/utils/SiteNavigation.java	30.00% <0.00%> (-50.00%)	7.00% <0.00%> (-10.00%)
...ommerce/core/search/internal/models/PagerImpl.java	44.44% <0.00%> (-50.00%)	8.00% <0.00%> (-11.00%)
...mponents/internal/models/v1/button/ButtonImpl.java	0.00% <0.00%> (-48.49%)	0.00% <0.00%> (-14.00%)
...ts/models/retriever/AbstractCategoryRetriever.java	37.50% <0.00%> (-45.00%)	6.00% <0.00%> (-8.00%)
...ls/v1/productcollection/ProductCollectionImpl.java	52.00% <0.00%> (-44.00%)	6.00% <0.00%> (-5.00%)
...l/services/GenericProductAttributeFilterInput.java	42.10% <0.00%> (-42.11%)	4.00% <0.00%> (-4.00%)
... and 36 more

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