[3.4] Add 'Maximum entities per datasource' parameter to widget configuration

[ikulikov]

General description

Add new Maximum entities per datasource parameter in the Data settings of widget configuration.
This allows to configure page size of widget subscription instead of using previously hardcoded value (1024).
See issue #6403.

Example of widget data settings

General checklist

• You have reviewed the guidelines document.
• PR name contains fix version. For example, "[3.3.4] Hotfix of some UI component" or "[3.4] New Super Feature".
• Description references specific issue.
• Description contains human-readable scope of changes.
• Description contains brief notes about what needs to be added to the documentation.
• No merge conflicts, commented blocks of code, code formatting issues.
• Changes are backward compatible or upgrade script is provided.
• Similar PR is opened for PE version to simplify merge. Required for internal contributors only.

Front-End feature checklist

• Screenshots with affected component(s) are added. The best option is to provide 2 screens: before and after changes;
• If you change the widget or other API, ensure it is backward-compatible or upgrade script is present.
• Ensure new API is documented here

Back-End feature checklist

• Added corresponding unit and/or integration test(s). Provide written explanation in the PR description if you have failed to add tests.
• If new dependency was added: the dependency tree is checked for conflicts.
• If new service was added: the service is marked with corresponding @TbCoreComponent, @TbRuleEngineComponent, @TbTransportComponent, etc.
• If new REST API was added: the RestClient.java was updated, issue for Python REST client is created.

[phamhaidang112000]

@ikulikov how to show widget data settings, please show me. I can't find it