Support for custom `context` provider about impress HOT 4 CLOSED

Now we have:

• per connection context and context.uuid autogenerated to identify connection context
• persistently stored context.session for whole session identified by context.session.token
• and context.session.accountId to identify certain user

See example: https://github.com/metarhia/Example/blob/34e4bb05b3048778c28dff675cfe64f9159b87d9/application/api/example.1/getClientInfo.js#L1-L9

I think we do not need session or connection bounded logger, because we use local logs for system logging, while for business-process logging we need separate place: Journal (system wide, single for all servers)

Also I do not think that we need database connection in context associated with certain transaction, we can do it in different way: any transaction should be started/committed/rolledback in a single routine, if we need to pass a reference to a connection to other procedures, we can do it manually, but I'd like to have start/commit/rollback in one place and use passed reference just for queries but not for doing operations with transaction.

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Also we do not need class or factory function for context, what we need is a schema and .d.ts typing

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Platform should catch all context identifiers like context.uuid when we

• throw
• return Error
• console.*
  and write to logs

Alternatively we can register ids manually:

• by context.tag: object
• or context.registerLogId('key', value)
• or console.registerLogId('key', value)

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Partially done in Version 3.0.0, other features requires consensus and we will open new issues for them

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