Make SubmittedJobGraphStore configurable

[Chen Qin]

​Hi there,

​I would like to propose/discuss median level refactor work to make
submittedJobGraphStore configurable and extensible.

The rationale behind is to allow users offload those meta data to durable
cross dc read after write strong consistency storage and decouple with zk
quorum.
​

https://issues.apache.org/jira/browse/FLINK-7106

<https://issues.apache.org/jira/browse/FLINK-7106>
New configurable setting in flink.conf
​ looks like following

g​
raph
​-s
tore:
​customized/zookeeper
g​
raph
​-s
tore​.class: xx.yy.MyS3SubmittedJobGraphStore​Imp

g​
raph
​-s
tore.
​endpoint
: s3.amazonaws.com
g​
raph
​-s
tore.path.root:
​s3:/
​
/
​my root/​

Thanks,
Chen