[Server] Restore durable subscriptions on Server Restart

[romanett]

Proposed changes

This PR Enables the Server to persist existing durable subscriptions (incl message queue) on a server shutdown (incl. MonitoredItems & event / datatchange queues). And restore them after a server restart.

The persisting is done by extending Subscription & MonitoredItem with a method that converts the internal state of the object into a format that can be json serialized.

For this Subscription has a new Method public IStoredSubscription ToStorableSubscription().
The IMonitoredItem interface is extended with a new Method IStoredMonitoredItem ToStorableMonitoredItem().
Both Subscription & Monitoreditem have a new constructor accepting an IStoredSubscription/IStoredMonitoredItem.

The MasterNodeManager has a new Method

public virtual void RestoreMonitoredItems(
     IList<IStoredMonitoredItem> itemsToRestore,
     IList<IMonitoredItem> monitoredItems,
     IUserIdentity savedOwnerIdentity)

Also INodeManager is extended with a new Method

 void RestoreMonitoredItems(
     IList<IStoredMonitoredItem> itemsToRestore,
     IList<IMonitoredItem> monitoredItems,
     IUserIdentity savedOwnerIdentity)

Those methods are only called (& need to be implemented) if durable subscriptions will be supported by the server.

They will be called by the SubscriptionManager on Startup if subscriptions to restore a found.

The SubscriptionManager has access to an Interface ISubscriptionStore that is registered globally in the server.

The Interface has methods for Storing & Restoring Subscriptions & providing access to durable queues after a restart.
In the reference server the SubscriptionStore impementation communicates with the IMonitoredItemQueueManager to store & restore durable queues.

On Shutdown the SubscriptionManager will initate the storing process if an ISubscriptionStore is registered & durable subscriptions are enabled & present on the server.

In the reference server the serializable objects are written into a file in the current exectuting directory.

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• Enhancement (non-breaking change which adds functionality)
• Test enhancement (non-breaking change to increase test coverage)
• Breaking change (fix or feature that would cause existing functionality to not work as expected, requires version increase of Nuget packages)
• Documentation Update (if none of the other choices apply)

Checklist

• I have read the CONTRIBUTING doc.
• I have signed the CLA.
• I ran tests locally with my changes, all passed.
• I fixed all failing tests in the CI pipelines.
• I fixed all introduced issues with CodeQL and LGTM.
• I have added tests that prove my fix is effective or that my feature works and increased code coverage.
• I have added necessary documentation (if appropriate).
• Any dependent changes have been merged and published in downstream modules.

Further comments

Open Issues:

• Restore of Event Filter fails with Opc.Ua.ServiceResultException: FilterOperand is not supported.

[codecov]

Codecov Report

Attention: Patch coverage is 79.62185% with 97 lines in your changes missing coverage. Please review.

Project coverage is 56.83%. Comparing base (ef9387b) to head (e764d0e).
Report is 4 commits behind head on master.

Files with missing lines	Patch %	Lines
...Server/Subscription/MonitoredItem/MonitoredItem.cs	73.63%	20 Missing and 9 partials ⚠️
...braries/Opc.Ua.Server/NodeManager/SamplingGroup.cs	0.00%	15 Missing ⚠️
...aries/Opc.Ua.Server/NodeManager/CoreNodeManager.cs	38.09%	9 Missing and 4 partials ⚠️
...ies/Opc.Ua.Server/NodeManager/MasterNodeManager.cs	71.79%	6 Missing and 5 partials ⚠️
.../Opc.Ua.Server/Subscription/SubscriptionManager.cs	81.03%	8 Missing and 3 partials ⚠️
...ies/Opc.Ua.Server/Diagnostics/CustomNodeManager.cs	85.45%	3 Missing and 5 partials ⚠️
.../Opc.Ua.Server/NodeManager/SamplingGroupManager.cs	0.00%	7 Missing ⚠️
...braries/Opc.Ua.Server/Subscription/Subscription.cs	97.74%	1 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3025      +/-   ##
==========================================
+ Coverage   56.70%   56.83%   +0.13%     
==========================================
  Files         356      357       +1     
  Lines       68110    68862     +752     
  Branches    13950    14133     +183     
==========================================
+ Hits        38619    39138     +519     
- Misses      25339    25528     +189     
- Partials     4152     4196      +44     

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[mrsuciu]

Overall looks good. See the comments.