Add User to Alerts, add filterby backendroles

[skkosuri-amzn]

Issue #, if available:
#6
Description of changes:

• Add User to Alert.
• Added option to enable filterby backend roles. This is useful when we want to show only the monitors/destinations/alerts created by users who belong same backend role.
• By default this filterby is disabled. To enable this

curl -X PUT "https://localhost:9200/_cluster/settings?pretty" -H 'Content-Type: application/json' -d'
{
    "persistent" : {
	"opendistro.alerting.filter_by_backend_roles" : true
    }
}
'

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@8dbefaf). Click here to learn what that means.
The diff coverage is 71.69%.

@@            Coverage Diff            @@
##             master     #264   +/-   ##
=========================================
  Coverage          ?   80.64%           
  Complexity        ?      199           
=========================================
  Files             ?      150           
  Lines             ?     5099           
  Branches          ?      670           
=========================================
  Hits              ?     4112           
  Misses            ?      627           
  Partials          ?      360           

Impacted Files	Coverage Δ	Complexity Δ
...endistroforelasticsearch/alerting/MonitorRunner.kt	76.31% <0.00%> (ø)	0.00 <0.00> (?)
...erting/transport/TransportGetDestinationsAction.kt	81.81% <0.00%> (ø)	0.00 <0.00> (?)
...ch/alerting/resthandler/RestSearchMonitorAction.kt	80.48% <57.14%> (ø)	0.00 <0.00> (?)
...search/alerting/resthandler/RestGetAlertsAction.kt	85.71% <58.33%> (ø)	0.00 <0.00> (?)
.../alerting/resthandler/RestGetDestinationsAction.kt	84.09% <61.53%> (ø)	0.00 <0.00> (?)
...rch/alerting/transport/TransportGetAlertsAction.kt	81.25% <70.00%> (ø)	0.00 <0.00> (?)
...opendistroforelasticsearch/alerting/model/Alert.kt	87.50% <75.00%> (ø)	0.00 <0.00> (?)
...ndistroforelasticsearch/alerting/AlertingPlugin.kt	90.81% <100.00%> (ø)	0.00 <0.00> (?)
...relasticsearch/alerting/action/GetAlertsRequest.kt	100.00% <100.00%> (ø)	0.00 <0.00> (?)
...icsearch/alerting/action/GetDestinationsRequest.kt	100.00% <100.00%> (ø)	0.00 <0.00> (?)
... and 1 more

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[qreshi]

Out of curiosity, what's the difference between the KEYSTORE_PASSWORD and KEYSTORE_KEYPASSWORD?

[lezzago]

Minor refactor comments, but they not related to the current PR, so I am fine with that refactor being done in a later PR.

[lezzago]

Lets remove these attributes since they are used for filtering the query. These query filters can be added to the attribute filter and we can change filter to be type: List<TermsQueryBuilder>

[lezzago]

Lets remove destinationId and destinationType since they are used for filtering the query. These query filters can be added to the attribute filter and we can change filter to be type: List<TermsQueryBuilder>

[qreshi]

Should the actual setting name match the naming change as well?

I.e

opendistro.alerting.filter_by_backend_roles

[skkosuri-amzn]

My bad, fixed.