Make `ci_structure.sql` to be equal

What does this MR do?

This is was of:

• taken from: !67326 (diffs)
• added necessary tests and copy-writes
• tried to be somehow backward compatible with current changes
• a step towards the #334881 (closed)
• is internal change since we are not yet using these changes outside of our group
• updates SchemaMigrations to support database.yml config entry
• symlinks relevant entries

Conformity

• I have included changelog trailers, or none are needed. (Does this MR need a changelog?)
• I have added/updated documentation, or it's not needed. (Is documentation required?)
• I have properly separated EE content from FOSS, or this MR is FOSS only. (Where should EE code go?)
• I have added information for database reviewers in the MR description, or it's not needed. (Does this MR have database related changes?)
• 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.
• This change is backwards compatible across updates, or this does not apply.