Add logging of per-context variables to logging system and network stack

[uhertlein]

This change adds a per-thread logging context to the logging system, which can be set by the user and will then be logged from all threads and tasks created with that context.

This is useful to correlate requests from the client to any network requests made based on that request.

The logging formatter must be set up by including a MessageFormatter::ElementType::ContextValue with the 'format' set to the context key to use:

using ElementT = olp::logging::MessageFormatter::ElementType;
std::vector<ElementT> elements = {
    ElementT(ElementType::Time, "%F %T"),
    ElementT(ElementType::TimeMs, ".%03u "),
    ElementT(ElementType::Level, "%s ["),
    ElementT(ElementType::ContextValue, X_CORRELATION_ID),
    ElementT(ElementType::Tag, "] %s: "),
    ElementT(ElementType::Message, "%s")
};

The log context must then be created and set up once manually from the top-most thread:

std::shared_ptr<olp::logging::LogContext>
createLogContext(const std::string& correlationID)
{
    auto context = std::make_shared<olp::logging::LogContext>();
    (*context)[X_CORRELATION_ID] = correlationID;

    return context;
}

The log context is stored for each thread, so whenever a new thread or task is created, this context must somehow be copied into the thread-local storage of that new thread.

For ThreadPoolTaskScheduler, the current log context is captured for the new task lambda and made active when the task is activated.

For NetworkCurl, the current log context is captured inside the RequestHandle on creation and subsequently made active whenever this request is processed.

Resolves: OLPEDGE-2893

[codecov]

Codecov Report

Attention: Patch coverage is 97.29730% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 81.59%. Comparing base (e2b4c85) to head (7eaf577).

Files	Patch %	Lines
olp-cpp-sdk-core/src/logging/LogContext.cpp	96.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1507      +/-   ##
==========================================
+ Coverage   81.50%   81.59%   +0.09%     
==========================================
  Files         341      342       +1     
  Lines       13417    13452      +35     
  Branches     1447     1449       +2     
==========================================
+ Hits        10935    10975      +40     
+ Misses       1904     1898       -6     
- Partials      578      579       +1     

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