Expose data for GraphQL queries in Repository & Blob header app

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Context

We want to minimise the data we pass through the HAML and inject into Vue components. Here's the spreadsheet with analysis (internal-only) of what we need and what is or is not exposed.

Needed changes

field name in HAML	is in GraphQL	Ruby reference	GraphQL reference	To do
project_root_path	FALSE	project_root_path		Needed on refSelector change. Expose on Project.
xcode_url	FALSE	xcode_url		Expose on Project
kerberos_url	FALSE	kerberos_url		Expose on Project
is_binary	FALSE	def binary?	SnippetBlob binary	Expose on RepositoryBlob