scr: 3.0rc2 release, variants and deps updates (#27178)
scr: 3.0rc2 release, variants and deps updates (#27178)

* scr: 3.0rc2 release, variants and deps updates

This adds 3.0rc2 release for end users to aid in testing scr for
upcoming 3.0 release.

Included in this change:
- Require most recent component versions for this release
- Add a variant for PDSH as it is now an optional dependency with
this release
- Add bbapi and datawarp (dw) variants
- bbapi_fallback variant now requires bbapi variant with latest
release
- Add variants to enable/disable examples and tests
- Add shared variant and current conflicts with ~shared
- Update cmake_args to account for added variants where needed

Additional updates:
- Add maintainers
- Use lists and for loops to clean up repetitive code involving all
components
- Use self.define and self.define_from_variant to clean up cmake_args
- Use consistent quoting throughout package

* Un-deprecate v2 and legacy

* Use new conditional variants
LLNL/spack,LLNL/spack,LLNL/spack,LLNL/spack,LLNL/spack