Created sensor cache class

Created sensor cache and sensor interface that needs to be
implemented by sensors.

Tested:
- Sensors created by sensor cache are stored and reused if
  there is try to access same sensor multiple times.
- All other units tests are passing

Change-Id: I552b2016bca4688e1b2a223297587826af256b54
Signed-off-by: Krzysztof Grobelny <krzysztof.grobelny@intel.com>
diff --git a/tests/meson.build b/tests/meson.build
index 32baaad..08a6e6c 100644
--- a/tests/meson.build
+++ b/tests/meson.build
@@ -25,7 +25,12 @@
         'telemetry-ut',
         [
             '../src/persistent_json_storage.cpp',
+            '../src/report.cpp',
+            '../src/report_manager.cpp',
+            '../src/sensor_cache.cpp',
             'src/test_persistent_json_storage.cpp',
+            'src/test_sensor_cache.cpp',
+            'src/utils/generate_unique_mock_id.cpp',
         ],
         dependencies: [
             boost,
@@ -35,6 +40,6 @@
             phosphor_logging,
             sdbusplus,
         ],
-        include_directories: '../src',
+        include_directories: ['../src', 'src']
     )
 )