Convert Discussion Block Mako Templates to Django Templates

[salman2013]

Description

Convert all discussion xblock mako templates in edx-platform to Django templates.
This aligns with the deprecation of mako and prepares the block for extraction.

I identify following files,

_discussion_inline.html‎
_discussion_inline_studio.html‎
_filter_dropdown.html
_thread_list_template.html
_underscore_templates.html‎
discussion_board_fragment.html‎

Tasks:

• Convert all mako templates to Django templates
• Render django template with resource loader.
• Fix all tests.

Acceptance Criteria

• Templates converted with minimal functional changes
• UI and behavior remain identical
• All unit and integration tests pass

[salman2013]

PR : openedx/edx-platform#37662

[salman2013]

There is some recursive methods in _filter_dropdown.html which need to convert from django into mako, i converted them but this is failing some tests so i moved this ticket back into progress.