Skip migrations based on the current metafield status

[kennyadsl]

Skip metafield migrations when:

• create: skip when metafield already exists
• update: skip when metafield doesn't exist
• remove: skip when metafield doesn't exist

Example of output:

Running Rails from: /path/to/app
== migrating ==================================================================
-- create_metafield(:article, :collection, :collection_reference)
-- Metafield custom:collection already exists for article, skipping creation
   -> 0.3110s
-- create_metafield(:article, :category, :single_line_text_field)
-- Metafield custom:category already exists for article, skipping creation
   -> 0.2828s
== migrated (0.6152s) =========================================================

== migrating ==================================================================
-- create_metafield(:article, :collection, :collection_reference)
-- Metafield custom:collection already exists for article, skipping creation
   -> 0.3480s
-- update_metafield(:article, :xyz)
-- Metafield custom:xyz not found for article, skipping update
   -> 0.3251s
-- remove_metafield(:article, :xyz_test)
-- Metafield custom:xyz_test not found for article, skipping deletion
   -> 0.2981s
== migrated (0.9743s) =======================================================

[gianlukk994]

Looks great! 🚀