Support Attribute Coercion to merge date-time attributes with date-time values a specified period of time before the present

[gunterze]

Support Attribute Coercion to merge date-time attributes with date-time values a specified period of time before the present.

Rationale:
Enables to supplement C-FIND RQ identifiers with date range matching keys to limit returned matches to entities not older than a specified period (e.g. one year)

Solved by dcm4che/dcm4che#1385 , e.g.

Archive Attribute Coercion Attributes:

Name	Value
Attribute Coercion URI	merge-attrs:xxx
DIMSE	C_FIND_RQ
DICOM Transfer Role	SCU
DICOM Attribute Coercion Parameters	StudyDate={now,date-P1Y,yyyyMMdd}-

to only match studies of last year.