[Fleet] Enable showing integration subcategories

[jen-huang]

Summary

Now that elastic/integrations#5123 and #153216 is complete, this PR enables the integration subcategories feature by default. Users will see a much shorter list of top-level integration categories when they land in Browse Integrations. Once the user clicks into a category, subcategories will be presented if there are any (see #148894 for more details).

With the associated changes now merged and enabling this flag, the list now looks like this initially:

And when clicking into a large category with subcategories:

[apmmachine]

🤖 GitHub comments

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Just comment with:

• /oblt-deploy : Deploy a Kibana instance using the Observability test environments.
• run elasticsearch-ci/docs : Re-trigger the docs validation. (use unformatted text in the comment!)

[elasticmachine]

Pinging @elastic/fleet (Team:Fleet)

[criamico]

LGTM

[kibana-ci]

💚 Build Succeeded

• Buildkite Build
• Commit: 099939f

Metrics [docs]

Unknown metric groups

ESLint disabled line counts

id	before	after	diff
securitySolution	433	436	+3

Total ESLint disabled count

id	before	after	diff
securitySolution	513	516	+3

History

• 💚 Build #115157 succeeded cb5e83a

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@elasticmachine merge upstream

cc @jen-huang