Add lightning and sandbox capability to OAuthJWT

[patricknomad]

Update the the OAuthJWT authentication type to work for Lightning, Lightning Sandboxes and the Developer Edition.

Lightning Example

config/forrest.php

return [
    // ...
    'credentials' => [
        'loginURL' => 'https://login.salesforce.com',
        'consumerKey' => '<YOUR_KEY_HERE>',
        'username' => '<EMAIL>',
        'privateKey' => '<PRIVATE_KEY>',
    ],

    'instanceURL' => 'https://<YOUR_ORG>.my.salesforce.com',
    // ...
];

Lightning Sandbox Example

config/forrest.php

return [
    // ...
    'credentials' => [
        'loginURL' => 'https://test.salesforce.com',
        'consumerKey' => '<YOUR_KEY_HERE>',
        'username' => '<EMAIL>.<SANDBOX_NAME>',
        'privateKey' => '<PRIVATE_KEY>',
    ],

    'instanceURL' => 'https://<YOUR_ORG>--<SANDBOX_NAME>.sandbox.my.salesforce.com',
    // ...
];

Salesforce Developer Edition Example

config/forrest.php return [

    // ...
    'credentials' => [
        'loginURL' => 'https://test.salesforce.com',
        'consumerKey' => '<YOUR_KEY_HERE>',
        'username' => '<EMAIL>',
        'privateKey' => '<PRIVATE_KEY>',
    ],

    'instanceURL' => 'https://<DEV_DOMAIN>.develop.my.salesforce.com',
    // ...
];

[wch-karol]

@omniphx & @patricknomad ⚠️ This PR make instanceURL setting required to have filled in case of OAuthJWT auth method. Otherwise it throws us an MissingTokenException in refresh/create token method. I suggest to add it somewhere to docs.

[wch-karol]

And maybe change comment here: https://github.com/omniphx/forrest/blob/96cbd606dcd496ce626da0353133c35ca6f49082/src/config/config.php#L80-L83 And maybe then create .env variable eg SF_INSTANCE_URL

[omniphx]

@wch-karol thanks for pointing this out. Just merged in a fix so that instanceURL is no longer required (v2.18.2). The method previously used in this PR would try to retrieve an instanceURL from the latest token (which if missing would throw the MissingTokenException). Obviously, that would always be the case when trying to authenticate for the first time.

Unfortunately, not the best approach but also not @patricknomad's fault. Just a misleading method name.

Also, added some documentation as you suggested.

Cheers!