Refactor SVG handling for loading indicator

[Shaharyar-WebDev]

Refactor loading indicator SVG handling to use a custom SVG if configured, otherwise use default SVG.

Description

Refactored generate_loading_indicator_html() to support a custom SVG
loading indicator via the filament.loading_indicator_svg config key.

Previously, the SVG was hardcoded inline. Now the function:

1. Builds the default SVG as before (no behaviour change if config is unset)
2. Checks config('filament.loading_indicator_svg') for a custom SVG string
3. If found, replaces the __attributes__ placeholder with the resolved
   ComponentAttributeBag attributes (classes, wire:loading, etc.) and
   returns that instead

This keeps full backwards compatibility — existing apps with no config
value set will see zero change in behaviour or appearance.

Visual changes

If a user sets loading_indicator_svg in
their filament.php config, their chosen SVG will render in place of
the default spinner.
See Visuals

Functional changes

• [] Code style has been fixed by running the composer cs command.
• [] Changes have been tested to not break existing functionality.
• [] Documentation is up-to-date.

[danharrin]

I don't think that a config file is suitable for this sort of change to be honest. How about we ask the user to bind an Htmlable object to the container via a specific interface from Filament, that receives the attributes object in the constructor?