Add format parameter to DatetimeRangeInput widget

[xavArtley]

fix #1848

[codecov]

Codecov Report

Merging #2043 (53c8781) into master (d0b4e52) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #2043   +/-   ##
=======================================
  Coverage   84.30%   84.30%           
=======================================
  Files         178      178           
  Lines       20611    20612    +1     
=======================================
+ Hits        17376    17377    +1     
  Misses       3235     3235           

Impacted Files	Coverage Δ
panel/widgets/input.py	95.84% <100.00%> (+0.01%)	⬆️

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