[master] Persist only SHA digest of PersonalAccessToken#token

app/models/concerns/token_authenticatable.rb

app/models/concerns/token_authenticatable_strategies/base.rb

...odels/concerns/token_authenticatable_strategies/digest.rb

...els/concerns/token_authenticatable_strategies/insecure.rb

app/models/personal_access_token.rb

app/models/user.rb

...unreleased/security-51113-hash_personal_access_tokens.yml

...80910153412_add_token_digest_to_personal_access_tokens.rb

...13_add_index_to_token_digest_on_personal_access_tokens.rb

.../20180913142237_schedule_digest_personal_access_tokens.rb

db/schema.rb

lib/gitlab/auth/user_auth_finders.rb

lib/gitlab/background_migration/digest_column.rb

lib/gitlab/crypto_helper.rb

lib/tasks/tokens.rake

spec/lib/gitlab/background_migration/digest_column_spec.rb

...migrations/schedule_digest_personal_access_tokens_spec.rb

spec/models/concerns/token_authenticatable_spec.rb

spec/models/personal_access_token_spec.rb

spec/models/user_spec.rb