Rename file to dir in Environment

[ruanwenjun]

Description

I find a TODO in Environment, this pr is used to fix this TODO.

Issues Resolved

Rename some method ended with file to dir, e.g. configFile to configDir.

Check List

• New functionality includes testing.
  • All tests pass
• New functionality has been documented.
  • New functionality has javadoc added
• Commits are signed per the DCO using --signoff

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[opensearch-ci-bot]

❌   Gradle Check failure 74508f8
Log 4100

Reports 4100

[dblock]

Looks like legit build failures:

> Task :example-plugins:custom-settings:compileJava FAILED
/var/CITOOL/workflow/OpenSearch_CI/PR_Checks/Gradle_Check/search/plugins/examples/custom-settings/src/main/java/org/opensearch/example/customsettings/ExampleCustomSettingsConfig.java:99: error: cannot find symbol
        final Path configDir = environment.configFile();
                                          ^
  symbol:   method configFile()
  location: variable environment of type Environment
1 error

[opensearch-ci-bot]

❌   Gradle Check failure b4434a1
Log 4173

Reports 4173

[opensearch-ci-bot]

✅   Gradle Check success ff7e704
Log 4182

Reports 4182