Refactor to centralize Job Specification properties for reusability across ingestion jobs

[chrajeshbabu]

Currently some of the the job specification properties are defined at each implementation of batch ingestion like

Hadoop job runner has defined the job spec constants in it's corresponding implementation:

public static final String SEGMENT_GENERATION_JOB_SPEC = "segmentGenerationJobSpec";

// Field names in job spec's executionFrameworkSpec/extraConfigs section
private static final String DEPS_JAR_DIR_FIELD = "dependencyJarDir";
private static final String STAGING_DIR_FIELD = "stagingDir";

Similarly spark ingestion runner also defined the same constants in its own classes

private static final Logger LOGGER = LoggerFactory.getLogger(SparkSegmentGenerationJobRunner.class);
private static final String DEPS_JAR_DIR = "dependencyJarDir";
private static final String STAGING_DIR = "stagingDir";

Better to centralize them at common place and reuse to avoid deviations in the future.