#173 Provide CopyPayloadKeyActionFactory from knotx-example

[marcinus]

Description

Brings CopyPayloadKeyActionFactory from knotx-example repository.
Registers the factory with name copy-payload-key on SPI.
Provides unit tests and README update.

Motivation and Context

Fixes #173.

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 not work as expected)

Checklist:

• I have read the CONTRIBUTING document.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.

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I hereby agree to the terms of the Knot.x Contributor License Agreement.

[marcinus]

Please update CHANGELOG.md before merging

[codecov]

Codecov Report

Merging #198 into master will increase coverage by 0.03%.
The diff coverage is 95.94%.

@@             Coverage Diff              @@
##             master     #198      +/-   ##
============================================
+ Coverage     92.03%   92.07%   +0.03%     
- Complexity     1877     1905      +28     
============================================
  Files           179      181       +2     
  Lines          7358     7432      +74     
  Branches        179      180       +1     
============================================
+ Hits           6772     6843      +71     
- Misses          499      502       +3     
  Partials         87       87              

Impacted Files	Coverage Δ	Complexity Δ
...ts/action/library/CopyPayloadKeyActionFactory.java	94.73% <94.73%> (ø)	9.00 <9.00> (?)
...ction/library/CopyPayloadKeyActionFactoryTest.java	96.36% <96.36%> (ø)	19.00 <19.00> (?)

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