Allow interface as dateadded

[TheKeymaster]

Purpose

If you have a custom DateTime object which extends from \DateTimeInterface you can not set a date value, as would result in a type error.

Approach

Instead of requiring an instance of \DateTime for \FINDOLOGIC\Export\Data\DateAdded::setDateValue, just require an instance of \DateTimeInterface.

Open Questions and Pre-Merge TODOs

• [x] composer lint and composer fix was executed.
• [x] Tests were written and pass with 100% coverage.
• [x] ~A issue with a detailed explanation of the problem/enhancement was created and linked.~ Such a simple change does not require any issue.

[TheKeymaster]

@howard can be reviewed when you have time.

[codecov-io]

Codecov Report

Merging #104 into develop will not change coverage. The diff coverage is 100%.

@@           Coverage Diff            @@
##             develop   #104   +/-   ##
========================================
  Coverage        100%   100%           
  Complexity       261    261           
========================================
  Files             49     49           
  Lines            685    686    +1     
========================================
+ Hits             685    686    +1

Impacted Files	Coverage Δ	Complexity Δ
src/FINDOLOGIC/Export/Data/DateAdded.php	100% <100%> (ø)	5 <1> (ø)	:arrow_down:
src/FINDOLOGIC/Export/Data/Item.php	100% <100%> (ø)	53 <1> (ø)	:arrow_down:

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[TheKeymaster]

@howard can be reviewed again.

[howard]

@DomBra Thanks for the contribution! Merged the changes - they will be part of the next release. If you have any immediate use for it, please let me know so I can expedite it.