Refactor keywords generation to use definitions

[lucernae]

• Use safe.definitions for dict keys
• Add flood event time extra_keywords
• Add optional event time zone extra_keywords

[codecov[bot]]

Codecov Report

Merging #206 into develop will decrease coverage by 2.55%. The diff coverage is 100%.

@@            Coverage Diff             @@
##           develop    #206      +/-   ##
==========================================
- Coverage    78.85%   76.3%   -2.56%     
==========================================
  Files           40      34       -6     
  Lines         1537    1017     -520     
  Branches        97      69      -28     
==========================================
- Hits          1212     776     -436     
+ Misses         266     201      -65     
+ Partials        59      40      -19

Impacted Files	Coverage Δ
src/realtime/flood/flood_hazard.py	91.83% <100%> (+0.17%)	:arrow_up:
src/realtime/ash/ash_hazard.py	92% <100%> (+0.08%)	:arrow_up:
src/realtime/tests/test_general_configuration.py
src/realtime/earthquake/tests/test_shake_hazard.py
src/realtime/celeryconfig_sample.py
src/realtime/ash/tests/test_ash_hazard.py

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[lucernae]

I will merge this