Clean up RuboCop config deprecation warnings

[wilfison]

Two small .rubocop.yml updates that remove deprecation warnings printed on every RuboCop run.

1. Use plugins instead of require for rubocop-performance

Loads rubocop-performance via the plugins: key instead of require:.

-require:
+plugins:
   - rubocop-performance

Since RuboCop 1.72, extensions that support the plugin API (such as rubocop-performance) are expected to be declared under plugins:. Keeping it under require: prints:

rubocop-performance extension supports plugin, specify `plugins: rubocop-performance`
instead of `require: rubocop-performance` in .rubocop.yml.

2. Rename Naming/PredicateName to Naming/PredicatePrefix

Updates the cop name to its current spelling.

-Naming/PredicateName:
+Naming/PredicatePrefix:
   Enabled: false

The cop was renamed in RuboCop, so the old name triggers:

Warning: The `Naming/PredicateName` cop has been renamed to `Naming/PredicatePrefix`.
(obsolete configuration found in .rubocop.yml, please update it)

Scope

Both changes only affect the development environment.