Add error attribute to metrics labels

[jedrivisser]

This PR allows you to add specific information about an error to a metric when it occurs. For instance the mysql error code.

An example implementation of the ErrorAttributesGetter function for mysql:

// For information on MySQL errors and mappings, see https://dev.mysql.com/doc/mysql-errors/5.7/en/server-error-reference.html
func MySQLErrorAttributesGetter(err error) []attribute.KeyValue {
	var mysqlError *mysql.MySQLError
	if errors.As(err, &mysqlError) {
		return []attribute.KeyValue{
			attribute.String("error_type", "mysql"),
			attribute.String("error_number", strconv.FormatUint(uint64(mysqlError.Number), 10)),
		}
	}

	return nil
}

This would be registered with:

driverName, err := otelsql.Register("mysql",otelsql.WithErrorAttributesGetter(MySQLErrorAttributesGetter))

It creates a metric that looks something like:

db_sql_latency_milliseconds_bucket{error_number="1062",error_type="mysql",method="sql.stmt.exec",otel_scope_name="github.com/XSAM/otelsql",otel_scope_version="0.36.0",status="error",le="100"} 1

instead of:

db_sql_latency_milliseconds_bucket{method="sql.stmt.exec",otel_scope_name="github.com/XSAM/otelsql",otel_scope_version="0.36.0",status="error",le="100"} 1

This allows us to use the error number to decide if an error is a critical error or one that is already being managed in code.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.2%. Comparing base (4fe3c27) to head (61a22fd).

Additional details and impacted files

@@           Coverage Diff           @@
##            main    #440     +/-   ##
=======================================
+ Coverage   84.0%   84.2%   +0.1%     
=======================================
  Files         14      14             
  Lines        798     805      +7     
=======================================
+ Hits         671     678      +7     
  Misses       103     103             
  Partials      24      24             

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[jedrivisser]

Added some more unit tests

[XSAM]

@jedrivisser, thanks for creating this PR.

This feature seems reasonable, but some comments need to be resolved before merging.

Please also update the CHANGELOG.me file.

[jedrivisser]

Thanks for the review! I think I have addressed all issues. Please let me know if I missed or misunderstood anything