Add intro to GitLab video link

What does this MR do?

Adds a link to the Introduction to GitLab webinar to the Learn GitLab with tutorials page on docs.gitlab.com.

This video provides foundational knowledge for teams who are new to GitLab. It contains around 45 minutes of condensed content, specifically designed for customers and users who are new to GitLab and DevOps workflows.

The video:

• Addresses the question "What is GitLab?" at 3m 00s: https://youtu.be/_4SmIyQ5eis?t=180

• Provides a step-by-step walkthrough of a best practice workflow for using GitLab, starting at 9m 33s: https://youtu.be/_4SmIyQ5eis?t=573

• Explains terminology and hierarchies in GitLab which are foundational for understanding how to use GitLab for your own workflows from 16m 37s: https://youtu.be/_4SmIyQ5eis?t=997

• Guides you through the GitLab UI to demonstrate a typical workflow from 32m 00s: https://youtu.be/_4SmIyQ5eis?t=1922

Note: The video references some features that not included in the Free tier such as Scoped Labels and epics.

Related issues

• Learnability: Structured Learning - The Basics --> Create content for 'What's GitLab?'
• Part 1. of Q1FY23 KR: Create, or source and edit 4 tutorials to address the needs we learned about in longitudinal research
• Q4FY2022 KR: Make it easier to find tutorials on docs.gitlab.com

Author's checklist

• Consider taking the GitLab Technical Writing Fundamentals course.
• Follow the:
  • Documentation process.
  • Documentation guidelines.
  • Style Guide.
• Ensure that the product tier badge is added to topic's h1.
• Request a review based on:
  • The documentation page's metadata.
  • The associated Technical Writer.

If you are only adding documentation, do not add any of the following labels:

• ~"frontend"
• ~"backend"
• ~"type::bug"
• ~"database"

These labels cause the MR to be added to code verification QA issues.

Review checklist

Documentation-related MRs should be reviewed by a Technical Writer for a non-blocking review, based on Documentation Guidelines and the Style Guide.

• If the content requires it, ensure the information is reviewed by a subject matter expert.
• Technical writer review items:
  • Ensure docs metadata is present and up-to-date.
  • Ensure the appropriate labels are added to this MR.
  • If relevant to this MR, ensure content topic type principles are in use, including:
    • The headings should be something you'd do a Google search for. Instead of Default behavior, say something like Default behavior when you close an issue.
    • The headings (other than the page title) should be active. Instead of Configuring GDK, say something like Configure GDK.
    • Any task steps should be written as a numbered list.
    • If the content still needs to be edited for topic types, you can create a follow-up issue with the docs-technical-debt label.
• Review by assigned maintainer, who can always request/require the reviews above. Maintainer's review can occur before or after a technical writer review.
• Ensure a release milestone is set.