get_maintainer: add --json output mode

get_maintainer: add --json output mode

Add a --json flag to get_maintainer.pl that emits structured JSON output,
making results machine-parseable for CI systems, IDE integrations, and
AI-assisted development tools.

The JSON output includes a maintainers array with structured name, email,
and role fields, plus optional arrays for scm, status, subsystem, web, and
bug information when those flags are enabled.

Normal text output behavior is completely unchanged when --json is not
specified.

Assisted-by: Claude:claude-opus-4-6
Link: https://lore.kernel.org/20260408194542.1354549-1-sashal@kernel.org
Signed-off-by: Sasha Levin <sashal@kernel.org>
Acked-by: Joe Perches <joe@perches.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>