Chore: Add file extensions to all imports

[Pezmc]

Description

See discussion in #1908.

Skipping file extensions is a web pack feature that's scheduled to be removed from standard ES modules.

In the new ES modules proposal file extensions are mandatory in import statements.
Being explicit, also enables better static code analysis, performed by tools like VSCode and ESLint

This PR:

• Adds extensions to all imports (not requires)
• Enables an ESLint rule (with autofix) to require file extensions
• Configures ESLint to require all files to resolve

Related Issue(s)

#1908

Checklist

• I have read the contribution guidelines
• Suitable unit/system level tests have been added and they pass
• Documentation has been updated
  • Upgrade instructions
  • Configuration details
  • Concepts
• Changes flowforge.yml?
  • Issue/PR raised on flowforge/helm to update ConfigMap Template
  • Issue/PR raised on flowforge/CloudProject to update values for Staging/Production

Labels

• Backport needed? -> add the backport label
• Includes a DB migration? -> add the area:migration label

[Steve-Mcl]

@Pezmc do you have 2 mins to discuss this PR please?

[Pezmc]

Tidy up bad eslint config! These lines are turning off the null rule, which wasn't doing anything.

[Steve-Mcl]

Following a review of the changes and a quick chat with @Pezmc I am personally very happy happy to see this work merged.