Automate setting the gradle-plugin attribute on the Bintray package during release promotion

[wilkinsona]

We can do it with curl. Something like this:

curl \
	-s \
	-u ${BINTRAY_USERNAME}:${BINTRAY_PASSWORD} \
	-H "Content-Type: application/json" \
	-d '[ { "name": "gradle-plugin", "values": ["org.springframework.boot:org.springframework.boot:spring-boot-gradle-plugin"] } ]' \
	-X POST \
	https://bintray.com/api/v1/packages/${BINTRAY_SUBJECT}/${BINTRAY_REPO}/org.springframework.boot/versions/${version}/attributes

[wilkinsona]

To help verify the above, here's the command I used to do it manually for the release of 2.0.5.RELEASE:

curl --user awilkinson:******** -X POST https://bintray.com/api/v1/packages/spring/jars/org.springframework.boot/versions/2.0.5.RELEASE/attributes -H 'Content-Type:application/json' -d '[ { "name": "gradle-plugin", "values": ["org.springframework.boot:org.springframework.boot:spring-boot-gradle-plugin"] } ]'