Adds new convenience methods

[kellymears]

In my Bedrock projects I typically extend the Config class with some simple static methods which I have found to have broad utility. It is the aim of this PR to have them integrated into the core Config class.

I think that they are a good fit for inclusion here as they promote readability while also not over-complicating or obscuring implementation details (a central tenant of the Bedrock project.)

Further I am happy to submit a PR to the Bedrock repo taking advantage of the features included here, should there be interest. Or, it could just be left to be adopted incrementally.

Note that I have not updated the test suite. Personally I think adding @covers annotations to the existing methods would be sufficient, since the new methods are simply wrapping existing methods.

Examples of the syntax this PR enables

/**
 * Configure auth keys and salts.
 */
Config::defineSet([
    'AUTH_KEY' => env('AUTH_KEY'),
    'AUTH_SALT' => env('AUTH_SALT'),
    'LOGGED_IN_KEY' => env('LOGGED_IN_KEY'),
    'LOGGED_IN_SALT' => env('LOGGED_IN_SALT'),
    'NONCE_KEY' => env('NONCE_KEY'),
    'NONCE_SALT' => env('NONCE_SALT'),
    'SECURE_AUTH_KEY' => env('SECURE_AUTH_KEY'),
    'SECURE_AUTH_SALT' => env('SECURE_AUTH_SALT'),
]);

if (Config::containsKey('DISPLAY_ERRORS')) {
    ini_set('display_errors', Config::get('DISPLAY_ERRORS'));
}

if (Config::containsKeys(['SENTRY_DSN', 'WP_ENV']) &&
    ! Config::is('WP_ENV', 'development')) {
    \Sentry\init([
        'dsn'         => Config::get('SENTRY_DSN'),
        'environment' => Config::get('WP_ENV'),
        'release'     => Config::get('GIT_SHA'),
        'error_types' => E_ALL & ~E_NOTICE & ~E_DEPRECATED,
    ]);
}

[coveralls]

Pull Request Test Coverage Report for Build 64

• 0 of 7 (0.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-29.2%) to 70.833%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/Config.php	0	7	0.0%
<!--	Total:	0	7

Totals
Change from base Build 61:	-29.2%
Covered Lines:	17
Relevant Lines:	24

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💛 - Coveralls