Add GM welcome message when installing or updating module

[Jagusti]

Type of change

• New feature (non-breaking change which adds functionality)
• Translation (updates existing localization strings or adds complete new language file)

Checklist:

• I have run linting on my code to follow the follow the style of this project.
• I have commented my code, particularly in hard-to-understand areas.
• My changes generate no new unhandled or unexpected warnings.
• My change requires an update to the documentation.

Related Issue(s)

Improves visibility of #193

Description

Motivation and context

• Makes it easier to update Toolkit Content when installing or updating the module.
• Provides a route to highlight key release updates and calls for feedback.

Summary of changes

• Adds new template and listeners for welcome chat message
• Adds and checks for new user flag (welcomeMessageShown)
• Adds new localisation strings
• Uses utility function to refreshTookitContent()

How has this been tested?

Development / Testing Environment

• Foundry VTT: v10.288
• WFRP4e System: v6.1.4
• GM Toolkit: v6.0.0, dev:a1981c7

Screen Capture