The move to an HTTPS URL for the xmlns:xslt identifier has the unwanted
side-effect of disabling indentation.
This commit moves back to an HTTPS URL. It also changes the indent size
to 2, aligning with the size used by all the other poms that are written
by the flatten plugin.
Closes gh-16466
Move projects to better reflect the way that Spring Boot is released.
The following projects are under `spring-boot-project`:
- `spring-boot`
- `spring-boot-autoconfigure`
- `spring-boot-tools`
- `spring-boot-starters`
- `spring-boot-actuator`
- `spring-boot-actuator-autoconfigure`
- `spring-boot-test`
- `spring-boot-test-autoconfigure`
- `spring-boot-devtools`
- `spring-boot-cli`
- `spring-boot-docs`
See gh-9316