Add ESLint rule for declaring constants before they are used

[ManpreetSL]

Summary

It improves readability to declare constants above the call site.

Approach

• [ ] Add an ESLint rule to make it mandatory for constants to be declared above where they are used
• [ ] Test that the rule works by using constants before their declaration point in the code

[ManpreetSL]

Once the ESLint config got sorted out properly, this was done automatically:

Therefore, we can drop this ticket.