added support for Collection Functions

new supported operations: min,max,sum,avg
new supported time scopes: interval,startup

added unit test to verify that each collection function returns correct
timestamp and value

Tested:
- POST/GET on telemetry features in bmcweb, no regression detected
- Using dbus API metric with collection function works as expected

Change-Id: Ib364c433915e07fd7a102f00109525362c40ab8a
Signed-off-by: Krzysztof Grobelny <krzysztof.grobelny@intel.com>
diff --git a/tests/meson.build b/tests/meson.build
index a3a78ec..3059953 100644
--- a/tests/meson.build
+++ b/tests/meson.build
@@ -11,6 +11,7 @@
     executable(
         'telemetry-ut',
         [
+            '../src/details/collection_function.cpp',
             '../src/discrete_threshold.cpp',
             '../src/metric.cpp',
             '../src/numeric_threshold.cpp',