story #7603: index tracker date fields

The fields cannot be searched upon yet but should be present within the elasticsearch database.
[You will probably need to reindex the whole tracker mapping]

Change-Id: I470a46b50349304d6c288e5657e6585cc6b472be
Merge commit 'refs/changes/76/3276/6' of ssh://gerrit.tuleap.net:29418/tuleap into tuleap-stable-master

* ssh://gerrit.tuleap.net:29418/tuleap:
  story #7603: index tracker date fields

Change-Id: I0a734cdacb0f0eb1d539df305dd9e67a5e60092b
This is Tuleap 7.7.99.43

Change-Id: If4b37fe1cf84e70054f9fd1fc930c69da2d9270d