fix: custom tab without entity error

[kkedziak-splunk]

Issue number: ADDON-80104

PR Type

What kind of change does this PR introduce?

• Feature
• Bug Fix
• Refactoring (no functional or API changes)
• Documentation Update
• Maintenance (dependency updates, CI, etc.)

Summary

Changes

Made entity as an optional attribute while accessing it from globalConfig. Also updated the documentation and added a customTab without entities in _everything add-on.

User experience

Now users can create their customTab without defining entity.

Checklist

If an item doesn't apply to your changes, leave it unchecked.

Review

• self-review - I have performed a self-review of this change according to the development guidelines
• Changes are documented. The documentation is understandable, examples work (more info)
• PR title and description follows the contributing principles
• meeting - I have scheduled a meeting or recorded a demo to explain these changes (if there is a video, put a link below and in the ticket)

Tests

See the testing doc.

• Unit - tests have been added/modified to cover the changes
• Smoke - tests have been added/modified to cover the changes
• UI - tests have been added/modified to cover the changes
• coverage - I have checked the code coverage of my changes (see more)

Demo/meeting:

Reviewers are encouraged to request meetings or demos if any part of the change is unclear

[github-actions]

Code Coverage ⚠️

Type	PR	Develop	Change	Status
Line Coverage	88.21%	88.27%	0.06%	🔴 Decreased
Branch Coverage	81.79%	81.92%	0.13%	🔴 Decreased