Add unique HTML IDs to admin settings forms

What does this MR do?

Adds unique values for the HTML id attributes of Rails-generated <form> elements.

Benefits

• clears up the warnings in the browser console, providing a better DX (Developer Experience)
• having valid HTML is always a plus -- non-unique id attribute values lead to invalid HTML

How to test

• go to Admin Area > Settings > General
• lo and behold the clean browser console!
• check out any other git branch and compare the browser console - now it's full of warnings

Screenshots

Before	After

Does this MR meet the acceptance criteria?

Conformity

• Code review guidelines
• Merge request performance guidelines
• Style guides