Make sure all YML files in Forum module has no type-casting to string.

Follow-up from #1653026: [META] Use properly typed values in module configuration.

Problem/Motivation

All integers, Booleans, and even octal numbers in config object files are converted to strings.

Proposed resolution

#1653026: [META] Use properly typed values in module configuration has fixed core, so no need to convert all data types to string anymore.

Remaining tasks

Fix and issue patch for below config files:
entity.display.taxonomy_term.forums.default.yml
entity.form_display.taxonomy_term.forums.default.yml
field.field.forum_container.yml
field.instance.taxonomy_term.forums.forum_container.yml
forum.settings.yml
node.type.forum.yml
rdf.mapping.node.forum.yml
rdf.mapping.taxonomy_term.forums.yml
views.view.test_forum_index.yml

User interface changes

NO

API changes

NO

Related Issues

Parent: #1653026: [META] Use properly typed values in module configuration