Unify error code for Persistent Storage Delegate

[jepenven-silabs]

Problem

When a value is not found two possible error code can be returned depending on implementation type :
CHIP_ERROR_PERSISTED_STORAGE_VALUE_NOT_FOUND and CHIP_ERROR_KEY_NOT_FOUND

Proposed Solution

Unify the API so that the same error code is return regardless of implementation.

[bzbarsky-apple]

So in particular, src/include/platform/KeyValueStoreManager.h documents that CHIP_ERROR_PERSISTED_STORAGE_VALUE_NOT_FOUND is used to represent "no value for this key" (for Get and Delete).

So does src/include/platform/PersistedStorage.h (for Read).

But src/lib/core/CHIPPersistentStorageDelegate.h does not document what error codes should be used for SyncGetKeyValue or SyncDeleteKeyValue.

Looking at the implementations, I see the following behavior for SyncGetKeyValue:

• TestCASESessionPersistentStorageDelegate: returns CHIP_ERROR_INTERNAL
• TestPersistentStorageDelegate: returns CHIP_ERROR_PERSISTED_STORAGE_VALUE_NOT_FOUND
• PersistentStorage (in examples/chip-tool/config/PersistentStorage.h): returns CHIP_ERROR_KEY_NOT_FOUND
• MyServerStorageDelegate (in examples/platform/linux/AppMain.cpp): calls through to KeyValueStoreMgr. Does not handle size inout param correctly...
• DeviceStorageDelegate: calls through to KeyValueStoreMgr
• AndroidDeviceControllerWrapper: Calls through to KeyValueStoreMgr
• PythonPersistentStorageDelegate: returns CHIP_ERROR_KEY_NOT_FOUND
• StorageAdapter (in python code): returns CHIP_ERROR_KEY_NOT_FOUND
• ServerStorageDelegate (in python code): calls through to KeyValueStoreMgr. Does not handle size inout param correctly...
• CHIPPersistentStorageDelegateBridge: returns CHIP_ERROR_KEY_NOT_FOUND

The implementations are also not consistent in terms of what they return when the buffer is too small.

We should align all of these with KeyValueStoreManager so calling through to that is sane.