entity-manager: move dbusMatches to class

```
static boost::container::flat_map<std::string, sdbusplus::bus::match_t>
        dbusMatches;
```
is moved to EntityManager class as
```
boost::container::flat_map<std::string, sdbusplus::bus::match_t>
        dbusMatches;
```
to get rid of the static variable.

Tested: on Tyan S8030. Matches are created without issue.
The debug level logging helps to confirm.

```
Jul 01 10:27:42 s8030-bmc-30303035c0c1 entity-manager[5010]: creating PropertiesChanged match on /xyz/openbmc_project/FruDevice/ConnectX_6_Dx_100GE_2P_NIC
Jul 01 10:27:42 s8030-bmc-30303035c0c1 entity-manager[5010]: creating PropertiesChanged match on /xyz/openbmc_project/FruDevice/PWS_920P_SQ
Jul 01 10:27:42 s8030-bmc-30303035c0c1 entity-manager[5010]: creating PropertiesChanged match on /xyz/openbmc_project/FruDevice/PWS_920P_SQ_0
Jul 01 10:27:42 s8030-bmc-30303035c0c1 entity-manager[5010]: creating PropertiesChanged match on /xyz/openbmc_project/FruDevice/S8030GM2NE
```

Change-Id: I9918f0f6e81aac55a174e3ee97e2cd7ff56ef2f3
Signed-off-by: Alexander Hansen <alexander.hansen@9elements.com>
diff --git a/src/entity_manager/entity_manager.hpp b/src/entity_manager/entity_manager.hpp
index fdcce53..cbb5f0a 100644
--- a/src/entity_manager/entity_manager.hpp
+++ b/src/entity_manager/entity_manager.hpp
@@ -82,6 +82,9 @@
     boost::asio::steady_timer propertiesChangedTimer;
     size_t propertiesChangedInstance = 0;
 
+    boost::container::flat_map<std::string, sdbusplus::bus::match_t>
+        dbusMatches;
+
     void startRemovedTimer(boost::asio::steady_timer& timer,
                            nlohmann::json& systemConfiguration);
 };