add an example for logs, closes #112

Author: duncanpo

examples/logs/README.md

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+# Logs Example
+This example shows how to emit logs in MATLAB code using OpenTelemetry. OpenTelemetry-Matlab supports logging either through its front-end API, or using existing logging functions together with an appender. This example shows logging through front-end API. Currently, there is not yet any appenders available in the package.
+* At the beginning of the first run, initialization is necessary to create and store a global logger provider.
+* At the beginning of each function, the global logger provider is used to create a logger.
+* Use the created logger to create and emit logs.
+
+## Running the Example
+1. Start an instance of [OpenTelemetry Collector](https://github.com/open-telemetry/opentelemetry-collector).
+2. Start MATLAB. 
+3. Ensure the installation directory of OpenTelemetry-matlab is on the MATLAB path.
+4. Run logs_example.

examples/logs/logs_example.m

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+function yf = logs_example
+% This example creates and emits logs from MATLAB code that fits a line 
+% through a cluster of data points. It create a log record for each
+% function call, and it also captures the parameters of the best fit line.
+
+% Copyright 2024 The MathWorks, Inc.
+
+% initialize logging during first run
+runOnce(@initLogger);
+
+% create a logger and start emitting logs
+lg = opentelemetry.logs.getLogger("logs_example");
+info(lg, "logs_example");
+
+[x, y] = generate_data();
+yf = best_fit_line(x,y);
+end
+
+function [x, y] = generate_data
+% generate some random data
+lg = opentelemetry.logs.getLogger("logs_example");
+info(lg, "generate_data");
+
+a = 1.5;
+b = 0.8;
+sigma = 5;
+x = 1:100;
+y = a * x + b + sigma * randn(1, 100);
+end
+
+function yf = best_fit_line(x, y)
+% fit a line through points defined by inputs x and y
+lg = opentelemetry.logs.getLogger("logs_example");
+info(lg, "best_fit_line");
+
+coefs = polyfit(x, y, 1);
+
+% capture the coefficients
+info(lg, coefs);
+
+yf = polyval(coefs , x);
+end
+
+function initLogger
+% set up global LoggerProvider
+resource = dictionary("service.name", "OpenTelemetry-Matlab_examples");
+lp = opentelemetry.sdk.logs.LoggerProvider(...
+    opentelemetry.sdk.logs.SimpleLogRecordProcessor, Resource=resource);
+setLoggerProvider(lp);
+end
+
+% This helper ensures the input function is only run once
+function runOnce(fh)
+persistent hasrun
+if isempty(hasrun)
+    feval(fh);
+    hasrun = 1;
+end
+end