Add Windows Services input plugin (#3023)

plugins/inputs/win_services/README.md

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+# Telegraf Plugin: win_services
+Input plugin to report Windows services info.
+
+It requires that Telegraf must be running under the administrator privileges.
+### Configuration:
+
+```toml
+[[inputs.win_services]]
+  ## Names of the services to monitor. Leave empty to monitor all the available services on the host
+  service_names = [
+    "LanmanServer",
+    "TermService",
+  ]
+```
+
+### Measurements & Fields:
+
+- win_services
+    - state : integer
+    - startup_mode : integer
+
+The `state` field can have the following values:
+- 1 - stopped
+- 2 - start pending
+- 3 - stop pending
+- 4 - running
+- 5 - continue pending
+- 6 - pause pending 
+- 7 - paused
+
+The `startup_mode` field can have the following values:
+- 0 - boot start
+- 1 - system start
+- 2 - auto start
+- 3 - demand start
+- 4 - disabled   
+
+### Tags:
+
+- All measurements have the following tags:
+    - service_name
+    - display_name
+
+### Example Output:
+```
+* Plugin: inputs.win_services, Collection 1
+> win_services,host=WIN2008R2H401,display_name=Server,service_name=LanmanServer state=4i,startup_mode=2i 1500040669000000000
+> win_services,display_name=Remote\ Desktop\ Services,service_name=TermService,host=WIN2008R2H401 state=1i,startup_mode=3i 1500040669000000000
+```
+### TICK Scripts
+
+A sample TICK script for a notification about a not running service.
+It sends a notification whenever any service changes its state to be not _running_ and when it changes that state back to _running_. 
+The notification is sent via an HTTP POST call.
+
+```
+stream
+    |from()
+        .database('telegraf')
+        .retentionPolicy('autogen')
+        .measurement('win_services')
+        .groupBy('host','service_name')
+    |alert()
+        .crit(lambda: "state" != 4)
+        .stateChangesOnly()
+        .message('Service {{ index .Tags "service_name" }} on Host {{ index .Tags "host" }} is in state {{ index .Fields "state" }} ')
+        .post('http://localhost:666/alert/service')
+```