Provide self-serve deletion method

What does this MR do?

!49626 (merged) increased the number of deletion requests 5 folds.

This MR adds wording to the GitLab.com account deletion section to provide a self-serve option when password is not set.

Additional context: we have received a large number of deletion requests and Support has been providing the self-serve method to users through responses in service desk. This provides the self-serve method upfront instead of finding out after writing into our service desk tracker.

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Conformity

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