Make Liquid TextEncoder configurable

[sfmskywalker]

Fixes #4380

This PR also changes from HtmlEncoder to NullEncoder by default.
To configure the default encoder, do this from Program.cs:

services.AddElsa(elsa => elsa.UseLiquid(liquid => liquid.FluidOptions => options => options.Encoder = HtmlEncoder.Default));

=== auto-pr-body ===

Summary:
This pull request refactors the existing LiquidFeature and LiquidTemplateManager classes, adds a new LiquidOptions class, and adds relevant using statements.

List of Changes:
-Added using statements for System.Text, System.Text.Encodings.Web, and Fluid to the Program.cs file.
-Added a new option to the LiquidFeature class to configure the Fluid options.
-Added a new options class LiquidOptions which includes a dictionary of Fluid filter registrations, parser configurations, and a flag for allowing access to configuration objects.
-Added a TextEncoder property to the LiquidOptions class.
-Changed LiquidParser to inherit from the Fluid Parser class.
-Removed the TextEncoder from the LiquidTemplateManager constructor and updated to use encoder property from the LiquidOptions.
-Renamed FluidOptions to LiquidOptions for consistency.
-Organized the new classes and using statements in Program.cs by namespace for clarity.
-Moved new options to an "options" folder in the Elsa.Liquid module.

Refactoring Target:
This pull request refactors the LiquidFeature and LiquidTemplateManager classes, adds a new LiquidOptions class, and adds relevant using statements.