[AIRFLOW-5583] Extend the "DAG Details" page to display the start_date / end_date

[visciang]

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[codecov-io]

Codecov Report

Merging #6235 into master will increase coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #6235      +/-   ##
==========================================
+ Coverage   80.05%   80.06%   +<.01%     
==========================================
  Files         610      610              
  Lines       35261    35261              
==========================================
+ Hits        28229    28230       +1     
+ Misses       7032     7031       -1

Impacted Files	Coverage Δ
airflow/utils/dag_processing.py	56.55% <0%> (-0.35%)	⬇️
airflow/models/taskinstance.py	93.75% <0%> (+0.5%)	⬆️

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[mik-laj]

@visciang This PR have a too much commits. Can you do a rebase?