adding back event_id and obs_id in dl1 tables

[vuillaut]

event_id and obs_id disappeared from the dl1 image table with ctapipe v0.8

add simple test to check if these parameters are present in the file after r0 to dl1

[codecov]

Codecov Report

Merging #546 into master will increase coverage by 0.10%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #546      +/-   ##
==========================================
+ Coverage   38.61%   38.72%   +0.10%     
==========================================
  Files          79       79              
  Lines        7077     7089      +12     
==========================================
+ Hits         2733     2745      +12     
  Misses       4344     4344              

Impacted Files	Coverage Δ
lstchain/io/io.py	80.95% <100.00%> (ø)
lstchain/reco/r0_to_dl1.py	62.37% <100.00%> (ø)
lstchain/tests/test_lstchain.py	100.00% <100.00%> (ø)

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