Migrations: Set users.following_count to NOT NULL

Also set following_count for local users to the correct value and for remote
users to 0.
9 jobs for bugfix/1447-set-following in 17 minutes (queued for 2 seconds)
Status Job ID Name Coverage
  Build
passed #80751
build

00:03:05

 
  Test
passed #80756
analysis

00:03:09

passed #80753
federated-testing

00:04:07

passed #80755
lint

00:00:20

passed #80752
unit-testing

00:02:56

86.7%
passed #80754
unit-testing-rum

00:05:22

 
  Benchmark
passed #80757
benchmark

00:08:31

 
  Deploy
manual #80758
allowed to fail manual
review_app
manual #80759
allowed to fail manual
stop_review_app