Add Issue Link to "Issue opened by" Integration Chat Message

What does this MR do?

We use the Discord integration for a #dev-log channel to log each commit, issue, and merge request in our project. Unfortunately, the message for opening issues is useless for us because it literally just contains the project name and Issue opened by <user>. Opposed to the closed message which also includes the link and title.

This MR adds the issue link, iid, and title to the "Issue opened by" integration message (NOT only Discord but probably all integrations).

Screenshots

Before
After
Reference (closed)

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• [-] Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• [-] Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• [-] Label as security and @ mention @gitlab-com/gl-security/appsec
• [-] The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• [-] Security reports checked/validated by a reviewer from the AppSec team