Add Template Parameters (-p) Feature

[julwrites]

Implemented support for dynamic Template Parameters (-p, --param) based on highest priority item in BACKLOG.md.

Changes:

1. lua/llm/config.lua: Added template_params table schema.
2. lua/llm/commands.lua: Implemented get_template_params_args() and included it in the command arguments stream for all prompt variants.
3. tests/spec/commands_spec.lua: Added busted tests for the new parameter generation.
4. BACKLOG.md: Removed Gap 2.

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PR created automatically by Jules for task 6388159725558964927 started by @julwrites

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