Customers feedback: update GitLab for Jira Cloud installation tab

Issue

Based on the customer's feedback, we should update the installation guidelines for our app on Atlassian marketplace.

The link to our app is following: https://marketplace.atlassian.com/apps/1221011/gitlab-for-jira-cloud?tab=installation&hosting=cloud

The current tab looks like following:

Proposal

• Update the installation tab to include content such as HOW TO INSTALL FOR SELF-MANAGED USER.
• Include the links to our guidelines if allowed:
  • https://docs.gitlab.com/ee/administration/settings/jira_cloud_app.html#connect-the-gitlab-for-jira-cloud-app
  • https://docs.gitlab.com/ee/administration/settings/jira_cloud_app.html#install-the-gitlab-for-jira-cloud-app-manually