Add config_options|variables to BuildMetadata

These are data columns that store runtime configuration
of build needed to execute it on runner and within pipeline.

The definition of this data is that once used, and when no longer
needed (due to retry capability) they can be freely removed.

They use `jsonb` on PostgreSQL, and `text` on MySQL (due to lacking
support for json datatype on old enough version).

app/models/ci/build.rb

@@ -924,12 +924,10 @@ module Ci
     # have the old integer only format. This method returns the retry option
     # normalized as a hash in 11.5+ format.
     def normalized_retry
-      value = options&.dig(:retry)
-
-      if value.is_a?(Integer)
-        { max: value }.with_indifferent_access
-      else
-        value || {}
+      strong_memoize(:normalized_retry) do
+        value = options&.dig(:retry)
+        value = value.is_a?(Integer) ? { max: value } : value.to_h
+        value.with_indifferent_access
       end
     end
 

doc/development/migration_style_guide.md

@@ -340,10 +340,10 @@ class AddOptionsToBuildMetadata < ActiveRecord::Migration[5.0]
 end
 ```
 
-On MySQL the `JSON` and `JSONB` is translated to `TEXT 1MB`, as `JSONB` is PostrgreSQL only feature.
+On MySQL the `JSON` and `JSONB` is translated to `TEXT 1MB`, as `JSONB` is PostgreSQL only feature.
 
-For above reason you have to use serializer to provide translation layer
-to support seamlessly PostgreSQL and MySQL:
+For above reason you have to use a serializer to provide a translation layer
+in order to support PostgreSQL and MySQL seamlessly:
 
 ```ruby
 class BuildMetadata