Add PreferredContentMode preference

[NiklasMerz]

Platforms affected

iOS

Motivation and Context

This adds a prefrence to the webview which is useful for iPads. Apple introduced a setting which by defaults changes the useragent of iPads from iPad to Macintosh to provide a "desktop browsing experience". The new preference allows to change the default value.

See original issue from IAB: apache/cordova-plugin-inappbrowser#687

Description

Changed like : apache/cordova-plugin-inappbrowser#688

Documenation: https://github.com/apache/cordova-docs/pull/1083

Testing

Automatic tests still pass. I found no automatic tests for preferences at build time.

I created a blank new app, added this platform and checked navigator.userAgent while changing the preference. It should be iPad for mobile and Macintosh for desktop.

Checklist

• [x] I've run the tests to see all new and existing tests pass
• [x] I added automated test coverage as appropriate for this change
• [x] Commit is prefixed with (platform) if this change only applies to one platform (e.g. (android))
• [x] If this Pull Request resolves an issue, I linked to the issue in the text above (and used the correct keyword to close issues using keywords)
• [x] I've updated the documentation if necessary

[codecov-commenter]

Codecov Report

Merging #886 into master will increase coverage by 1.89%. The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #886      +/-   ##
==========================================
+ Coverage   74.40%   76.30%   +1.89%     
==========================================
  Files          13       13              
  Lines        1676     1941     +265     
==========================================
+ Hits         1247     1481     +234     
- Misses        429      460      +31     

Impacted Files	Coverage Δ
bin/templates/scripts/cordova/lib/prepare.js	86.60% <0.00%> (+1.19%)	:arrow_up:

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