Add links to Learn WordPress in the wp-admin Help box and the default comment

[kaitohm]

Training and Meta relaunched ​https://learn.wordpress.org/ in August this year. Training has since been discussing how we can increase traffic to the site, especially from within the WordPress software. (See discussions ​Drawing new learners to the new Learn.WordPress.org, which led to ​Brainstorm: Introducing Learning Pathways to users during onboarding.)

Previously, there have been ideas to add/revamp dashboard widgets that link to Learn WordPress resources. ticket:50139 ticket:57785 ticket:61585

Here, we propose two new ideas that do not rely on the use of widgets.

1. Add a reference to Learn in the Help box

Currently, "Support Forums" links to the general landing page ​https://wordpress.org/support/forums/ or its locale equivalent. We suggest adding "Learning resources on Learn WordPress" or similar, which links to ​https://learn.wordpress.org/ under that.

2. Add a reference to the WordPress User courses in the default comment on a new install

Currently, the auto-generated comment on a new install says:

Hi, this is a comment.
To get started with moderating, editing, and deleting comments, please visit the Comments screen in the dashboard.
Commenter avatars come from ​Gravatar.

We would like to add something along these lines to that comment.

If you're new to WordPress, check out these free courses by the official WordPress
Training Team: ​The WordPress User Learning Pathway

Trac ticket: #62510

## Description
This PR adds Learn WordPress links to improve resource discoverability in two locations:

1. The wp-admin Help panel
2. The default comment text

## Why

• Helps users discover official WordPress learning resources more easily
• Provides direct access to learning materials from within wp-admin

Hi @kaitohm,
I have made the changes requested please have a look at it at your convenience.
Thank you!