Ability to pass in extra contexts for liquid templates

[ribose-jeffreylau]

Motivation

In the process of converting existing Jekyll liquid templates into Relaton's vanilla liquid templates, I found the need to supply data that was not provided in build_liquid_document():

relaton-cli/lib/relaton/cli/xml_to_html_renderer.rb

Lines 54 to 62 in 1c5170d

	hash_to_liquid(
	depth: 2,
	css: stylesheet,
	title: bibcollection.title,
	date: Date.today.to_s,
	metanorma_v: mnv.lines.first&.strip,
	author: bibcollection.author,
	documents: document_items(bibcollection)
	)

Examples include the domain name of the deployed site, for the construction of the canonical URL link element.

Proposals

A. Add a CLI param that accepts a YAML / JSON file, which will be merged into the arguments for hash_to_liquid(...), making its contents available inside custom liquid templates.
B. Allow contents from metanorma.yml to be passed to hash_to_liquid(...).

To me, proposal B sounded simpler (initially), but metanorma.yml is not an input of Relaton, so the proposal reduces to proposal A.