Several reactive starters do not depend on spring-boot-reactor

[kzander91]

I noticed this while troubleshooting why spring.reactor.context-propagation=auto wasn't working for me after upgrading to 4.0.

IMHO, all starters for reactive technologies should also bring in Boot's reactor module.

[bclozel]

I've collected the list of reactive starters and whether they already depend on spring-boot-reactor, we are missing a few.

Starter	Depends on spring-boot-reactor
spring-boot-starter-reactor-netty	Yes
spring-boot-starter-webclient	No
spring-boot-starter-graphql	No
spring-boot-starter-webflux	No
spring-boot-starter-data-cassandra-reactive	Yes
spring-boot-starter-data-couchbase-reactive	Yes
spring-boot-starter-data-mongodb-reactive	Yes
spring-boot-starter-data-r2dbc	Yes
spring-boot-starter-data-redis-reactive	Yes
spring-boot-starter-rsocket	No