Add limit for group count within namespaces

What does this MR do and why?

Add limit as popover for group dependencies project search.

EE: true Changelog: changed

Based on this comment and this issue.

Screenshots or screen recordings

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Under the limit	Over the limit

Query plan

The query plan bellow uses the group with highest count, i.e., 1683

Link to the query plan

SELECT COUNT(*) FROM "namespaces" WHERE "namespaces"."type" = 'Group' AND (traversal_ids @> ARRAY[6543]);

How to set up and validate locally

1. Fetch the content of both branches: add_limit_for_group_count.
2. Turn on the feature flag to make Dependency list appear in groups:

echo "Feature.enable(:group_level_dependencies)" | rails c

3. Create two projects under a group with the following content:

• .gitlab-ci.yml:

include:
  - template: Security/Dependency-Scanning.gitlab-ci.yml

• Gemfile.lock: with this content

4. Run a pipeline for the default branch to both projects
5. Go group related to the projects created above and click on the menu option Secure -> Dependency list
6. Change GROUP_COUNT_LIMIT to 1 in order to trigger the over the limit behaviour.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.