show applications table for every namespace when empty

[psanghvi17]

PR Checklist

• Linting Test is passing
• Code is well documented
• If applicable, a PR in the epinio/docs repository has been opened

Summary

Fixes #
Show the applications table for each namespace even when it has no applications, so users can confirm the namespace exists and see a consistent layout.

Occurred changes and/or fixed issues

1. Applications index grouping: Updated groupedByNamespace on the applications page to build groups from all namespaces (respecting the active namespace filter), not only from namespaces that currently have apps.
2. Empty-namespace tables: Ensured every visible namespace renders an applications DataTable, even when its app list is empty (table shows the standard “No data available” empty state).
3. Data loading: Added a findAll call for namespaces when loading the applications page so namespace data is always available for grouping.
4. UX consistency: Prevents confusion where a user selects/filters to a namespace but sees no applications section and assumes the namespace does not exist.

Technical notes summary

groupedByNamespace now:
Reads all namespaces via store.getters'epinio/all'.
Derives the set of namespaces to display based on activeNamespaceCache (or all when no filter is active).
Initializes an empty array for each of those namespaces and then assigns apps into the appropriate group.
Falls back to a single workspace group when nothing is yet loaded, preserving prior behavior.
Namespaces are explicitly fetched on mount of the applications page to keep grouping logic in sync with the current filter state.

Areas or cases that should be tested

Namespace with zero apps
Create a new namespace without deploying any applications.
Open the applications page and confirm the new namespace appears with an empty table.
Applications page – no filter
Navigate to the cluster applications page with multiple namespaces, some with apps and some without.
Verify that every namespace appears with a titled applications table; namespaces with no apps show the empty state row instead of no table.

Areas which could experience regressions

Namespace filtering logic: The applications page now depends more directly on activeNamespaceCache and namespace data; incorrect cache state or missing namespace fetch could affect which groups are rendered.
Applications page performance: The additional findAll call for namespaces runs on mount; though lightweight, any issues in that request could affect initial load time or error handling

Screenshot/Video