Duplicate Tag Exception while Publishing a portlet on a migrated System

Issue

After having upgraded from 6.2 to DXP Cloud or Liferay DXP 7.0+ with staging enabled and tagged web content articles, trying to publish the articles to Live results in the following error:

An unexpected error occurred with the publication process. Please check your portal and publishing configuration.

The Tag tagname could not be imported because of the following error: A tag with the name tagname (duplicate) already exists.

Environment

DXP 7.0+

Resolution

Create a portlet-ext.properties file in
[Liferay_Home]/tomcat-9.0.17/webapps/ROOT/WEB-INF/classes
Add the following line:
```
staging.merge.tags.by.name=true
```

This property is set to false by default because there are a couple of examples where merging the tags could potentially become a problem.
E.g.:
- There is a tag - belonging to an asset - that was already imported once.
  It is possible that the imported tag is renamed on the target site, and a similar one is created again. Then, you can decide to reimport the .lar file. If the property is set to false, reimporting the .lar file will not change the tag (that belongs to the asset), the old (renamed) one will remain.
- Tags are identified using their UUID, so the property ignores those and uses the name to identify the tags during the import.
  Most entities in Liferay are identified based on their UUID, so having an option to use names instead is not considered default.