Allow changing resource ID in offline approvals and document default value

[petrdvorak]

The SDK uses the /operation/authorize/offline value, but this is not mentioned anywhere in the docs. Therefore, the developers who build the server-side part themselves have hard time figuring out how the set the server-side constant and usually make a wrong guess. We should:

• Add the default value to the client-side documentation
• Allow changing the constant in the SDK

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Document Details

Do not edit this section. We use it to link the issue to the appropriate document. ⚠

• File: https://github.com/wultra/mtoken-sdk-ios/blob/releases/1.4.x/docs/Using-Operations-Service.md
• Timestamp: 1636019971