Allow updateMap to use custom sourceFile and mappingFile

[fanny-jiang]

What this PR does / why we need it:

Add support to the -updateMap flag to update provided mappingFile with a provided sourceFile so that it can be used more generically in development and CI.

Which issue this PR fixes

(optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close that issue when PR gets merged)

• fixes #

Special notes for your reviewer:

QA

• Uncomment line 295 to print tmp file paths and build yaml-mapper binary
• ./yaml-mapper -updateMap with no flags should update default mappingFile with values from the latest Datadog chart values.yaml:
  • Remove a few unmapped helm keys from mapping_datadog_helm_to_datadogagent_crd.yaml and run ./yaml-mapper -updateMap. The helm keys should be added back to the default mapping file. (i.e. remove agents.containers.agent.envDict: "")
  • temp chart.yaml and datadog-values.yaml files should get cleaned up
• ./yaml-mapper -updateMap -sourceFile=<path-to-local-helm-charts-dir>/charts/datadog/values.yaml should update the default mappingFile with any new keys added to the local values.yaml file
• ./yaml-mapper -updateMap -sourceFile=<path-to-local-helm-charts-dir>/charts/datadog/values.yaml -mappingFile=<other-mapping-file> should update provided mappingFile with keys from the local values.yaml file
• ./yaml-mapper -updateMap -sourceFile=<any.yaml> -mappingFile=<some-mapping-file> should map keys from any yaml file to a provided mapping file
• For the above testing where -sourceFile flag is used , make sure provided sourceFile doesn't get deleted!
• values.yaml => DDA mapping should be unaffected

Checklist

[Place an '[x]' (no spaces) in all applicable fields. Please remove unrelated fields.]

• Chart Version bumped
• Documentation has been updated with helm-docs (run: .github/helm-docs.sh)
• CHANGELOG.md has been updated
• Variables are documented in the README.md
• For Datadog Operator chart or value changes update the test baselines (run: make update-test-baselines)