Add InstaWP GitHub Action

[merkushin]

We add an InstaWP GitHub Action for creating a website for each pull request.
In this configuration, it won't update a website on the PR update.
But it will destroy the website once the PR was merged or closed.
The website will be deleted automatically after 15 days.

Changes proposed in this Pull Request

• Add configuration for the InstaWP GitHub Action.

Testing instructions

• It must add a comment to the PR with links to the created website and for the auto-login.
• Find those links and follow them :)

Screenshot / Video

[codecov]

Codecov Report

Merging #6187 (80432ec) into trunk (7dbccb4) will not change coverage.
Report is 1 commits behind head on trunk.
The diff coverage is n/a.

@@            Coverage Diff            @@
##              trunk    #6187   +/-   ##
=========================================
  Coverage     48.07%   48.07%           
  Complexity    10467    10467           
=========================================
  Files           573      573           
  Lines         44164    44164           
  Branches        402      402           
=========================================
  Hits          21234    21234           
  Misses        22603    22603           
  Partials        327      327           

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[merkushin]

We decided to use Playground for this purpose.