Split out standard variants from reserved

[rfbgo]

This changes how validate_variant works and allows standard variants (eg containerized) to be declared via variant

[ramble-project-pr-bot]

Ramble Performance Test Metrics

Results produced with commit: b2a1943

Test Name	Outcome	Duration (s)	Most Recent Run (s)	Last 5 Avg (s)
test_analyze_large_file	passed	1.0411	1.0900 (87a758d)	1.0791
test_large_template_expansion	passed	1.1624	1.2086 (87a758d)	1.2154
test_many_experiments	passed	29.4395	29.0202 (87a758d)	29.4632
test_many_objects_defaults	passed	15.0905	15.1380 (87a758d)	15.8150
test_matrix_filter_perf	passed	1.0373	1.0573 (87a758d)	1.0991

[codecov]

Codecov Report

❌ Patch coverage is 95.71429% with 3 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
lib/ramble/ramble/variants.py	89.28%	3 Missing ⚠️

📢 Thoughts on this report? Let us know!