Update fallback sorting option on groups/project list to created

What does this MR do and why?

• Update the fallback sorting option on groups and projects list to be created. This is more optimal as we're missing an index on updated_at column (will be handled separately)
• Align the constant values to with the values from the backend (app/helpers/sorting_titles_values_helper.rb)
  • created_at to created
  • updated_at to updated

References

Related to #590893 (closed)

Screenshots or screen recordings

N/A

How to set up and validate locally

1. Enable explore_groups_vue feature flag
2. Go to /explore/groups and verify that the default sorting option is created_desc

MR acceptance checklist

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