Switch to using SAMMI for CDF attribute management (#1122)

* updating dependencies

* Move to SAMMI, fix all non-ISTP related errors

* Fixing ISTP errors and other bugs

* fix mag attrs

* fixing test

imap_processing/cdf/config/imap_ultra_l1a_variable_attrs.yaml

@@ -25,6 +25,7 @@ ultra_support_attrs:
   VALIDMAX: 9223372036854775807
   VAR_TYPE: support_data
   DISPLAY_TYPE: time_series
+  DEPEND_0: epoch
 
 string_base_attrs:
   CATDESC: string metadata

imap_processing/cdf/config/imap_variable_schema.yaml

@@ -0,0 +1,13 @@
+# This file acts as an overwrite option for the variable schema described by SAMMI.
+# SAMMI generally has good defaults and its schema should be used, but this is a place
+# to override those defaults if necessary.
+
+# This is only required while issue #7 is incomplete.
+attribute_key:
+  LABLAXIS:
+      description: >
+        should be a short character string (approximately 10 characters, but preferably 6 characters - more only if absolutely required for clarity) which can be used to label a y-axis for a plot or to provide a heading for a data listing.
+        Only one of LABLAXIS or LABL_PTR_i should be present.
+      required: false # not required if using LABL_PTR_i
+      valid_values: null
+      alternate: LABL_PTR_1