Added better support for naming releases

- Name can now be changed in the config without affecting previous
  versions
- Create release now allows --name to specify a different name than what
  is in the config
- Added migration to change the releases & dev_releases dirs to have
  sub-dirs for each release name

[#72994716]

Signed-off-by: Phan Le <ple@pivotallabs.com>
Improved integration test coverage for named releases

Signed-off-by: Phan Le <ple@pivotallabs.com>
Split release.rb into command specific files.

Signed-off-by: Phan Le <ple@pivotallabs.com>