Refactor/delete `RELEASING.md` in each repo

[mkurz]

Some repos contain a RELEASING.md file (not all repos). Some still mention travis, some even bintray 🤯

Suggestion: Let's create just one RELEASING.md in the https://github.com/playframework/.github repo and in every README.md in each repo we just refer to that file, like

// README.md
...
## Releasing

See https://github.com/playframework/.github/blob/main/RELEASING.md
...

Text for RELEASING.md should be:

• explain release by tag
• best release process IMHO is to git tag locally, then push the tag, wait if the workflow is running and if there is an error, if everything was ok, make a GitHub release (I think this is better than just creating a release with a new tag from the GitHub UI, because in case a problem occurs and the release fails, people already got a GitHub notification for the new release).

Repositories

• [x] playframework

• [x] playframework.com

• [x] interplay

• [x] play-doc

• [x] play-ebean

• [x] play-file-watch

• [x] play-grpc

• [x] play-json

• [x] play-mailer

• [x] play-samples

• [x] play-slick

• [x] play-soap

• [x] play-socket.io

• [x] play-webgoat

• [x] play-ws

• [x] anorm

• [x] cachecontrol

• [x] netty-reactive-streams

• [x] omnidoc

• [x] scalatestplus-play

• [x] twirl

• [x] play-java-seed.g8

• [x] play-scala-seed.g8

• [x] play-java-react-seed

• [x] play-scala-react-seed

• [x] play-java-angular-seed

• [x] play-scala-angular-seed

• [x] .github

• [x] play-meta

• [x] play-generated-docs

[ihostage]

That's exactly for such issues I created a new template 😂

[mkurz]

This is now done (of course the RELEASING.md still needs work :wink: )