refactor: make object tag permission checks modular

[wgu-taylor-payne]

Description

Refactor ObjectTagView and related serializers (ObjectTagMinimalSerializer, ObjectTagsByTaxonomySerializer) so that permission checks can be overridden by subclasses.

Functionality remains the same, but permission checks have been pulled out to make thing more modular and extensible.

Context

This comes out of the effort to update course authoring with openedx-authz based permissions and arose out of work on openedx/openedx-platform#38143.

Replaces #541.

Notes

GitHub Copilot with GPT-4.1 was used to aid development.

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