Feature/1292 enhance readability of dataextension retention policy

[JoernBerkefeld]

PR details

What changes did you make? (Give an overview)

• closes [FEATURE] enhance readability of dataExtension retention policy #1292

Further details (optional)

...

Checklist

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• test scripts updated
• Wiki updated (if applicable)

[github-actions]

Coverage Report

Commit:648d31b
Base: develop@a0c5996

Type	Base	This PR
Total Statements Coverage	65.8%	65.86%  (+0.06%)
Total Branches Coverage	66.85%	66.88%  (+0.03%)
Total Functions Coverage	75.45%	75.45%  (+0%)
Total Lines Coverage	65.8%	65.86%  (+0.06%)

Details (changed files):

File	Statements	Branches	Functions	Lines
lib/metadataTypes/DataExtension.js	79.46%	67.24%	94.28%	79.46%
lib/metadataTypes/Event.js	51.94%	100%	10%	51.94%