fix(a11y): mark edit-metadata header row with role=row and columnheader

Author: milanmajchrak

.gitignore

@@ -42,3 +42,5 @@ package-lock.json
 junit.xml
 
 /src/mirador-viewer/config.local.js
+
+FIX-PROGRESS.md

src/app/dso-shared/dso-edit-metadata/dso-edit-metadata-headers/dso-edit-metadata-headers.component.html

@@ -1,6 +1,6 @@
-<div class="d-flex flex-row ds-field-row ds-header-row">
-  <div class="lbl-cell">{{ dsoType + '.edit.metadata.headers.field' | translate }}</div>
-  <div class="flex-grow-1">
+<div class="d-flex flex-row ds-field-row ds-header-row" role="row">
+  <div class="lbl-cell" role="columnheader">{{ dsoType + '.edit.metadata.headers.field' | translate }}</div>
+  <div class="flex-grow-1" role="columnheader">
     <div class="d-flex flex-row">
       <div class="flex-grow-1 ds-flex-cell ds-value-cell"><b class="dont-break-out preserve-line-breaks">{{ dsoType + '.edit.metadata.headers.value' | translate }}</b></div>
       <div class="ds-flex-cell ds-lang-cell"><b>{{ dsoType + '.edit.metadata.headers.language' | translate }}</b></div>