make help should list AzureTRE commands as well

[LizaShak]

Description

Currently the only commands returned by make help are repository specific commands. It would be good to have a custom help command that merges help messages from both the repository-specific Makefile and the AzureTRE Makefile. This allow developers to quickly identify and understand the available make commands and their descriptions.

Acceptance Criteria

• The Makefile should include a help command that outputs help messages from both the current Makefile and the AzureTRE Makefile.
• The help command should format the output for readability.