Add security policy for Pleroma backend

Closes #1848
12 jobs for security-policy in 22 minutes and 29 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Build
passed #142968
build

00:07:19

 
  Test
passed #142973
analysis

00:03:22

passed #142970
federated-testing

00:05:59

passed #142972
lint

00:00:24

passed #143011
unit-testing

00:07:46

88.1%
passed #142971
unit-testing-rum

00:07:23

failed #142988
unit-testing

00:07:16

88.1%
failed #142986
unit-testing

00:07:14

88.1%
failed #142969
unit-testing

00:07:49

88.1%
 
  Benchmark
manual #142974
allowed to fail manual
benchmark
 
  Deploy
manual #142975
allowed to fail manual
review_app
manual #142976
allowed to fail manual
stop_review_app