Fix Gitpod url in user preferences

What does this MR do?

When the Gitpod integration is enabled (in the Admin Settings), inside the User Preferences we show a new setting to allow the user opt in and enable the integration as well. This setting includes a text which contains a link to the Gitpod url.

At the moment that url is hardcoded to https://gitpod.io but, since we have to configure a proper url in the Admin settings, that url should change to the configured one.

Screenshots (strongly suggested)

After the MR, the configured url in the Admin settings is used in the message:

Does this MR meet the acceptance criteria?

Conformity

• I have included a changelog entry, or it's not needed. (Does this MR need a changelog?)
• I have properly separated EE content from FOSS, or this MR is FOSS only. (Where should EE code go?)
• I have self-reviewed this MR per code review guidelines.
• This MR does not harm performance, or I have asked a reviewer to help assess the performance impact. (Merge request performance guidelines)
• I have followed the style guides.

Related to #321544 (closed)