Add user defined pod labels

[pdrastil]

This adds the ability to define user labels on Spark operator pod. Main use case is integration with external logging solution. Please let me know if I should bump chart version in the PR or if you manage release cycle for the chart. Thanks

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[pdrastil]

@googlebot I signed it!

[liyinan926]

Can you update the Chart readme and also bump the chart version?

[pdrastil]

Updated README and minor chart version.

[pdrastil]

@liyinan926 Hi, can you please check what's with your test cluster that is used for pre-commit checks? It seems that scheduler cannot find any nodes for spark-operator.