Update postgres deployment definition

[alfonsosanchezbeato]

K8s 1.16 wants a selector field.

[codecov-io]

Codecov Report

Merging #1 into master will decrease coverage by 0.84%. The diff coverage is n/a.

@@            Coverage Diff             @@
##           master       #1      +/-   ##
==========================================
- Coverage   83.88%   83.04%   -0.85%     
==========================================
  Files          38       38              
  Lines        1421     1421              
==========================================
- Hits         1192     1180      -12     
- Misses        173      185      +12     
  Partials       56       56

Impacted Files	Coverage Δ
identityapi/identityapi.go	12.5% <0%> (-9.73%)	:arrow_down:
identityapi/device.go	0% <0%> (ø)	:arrow_up:
service/manage/device.go	100% <0%> (ø)	:arrow_up:

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[slimjim777]

Thanks!