Update import to Strings in response to #9103 from core

[cwperks]

Description

Updates imports to Strings in CronSchedule and IntervalSchedule in response to opensearch-project/OpenSearch#9103

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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[cwperks]

The last core SNAPSHOT was published on Friday: https://aws.oss.sonatype.org/content/repositories/snapshots/org/opensearch/opensearch-core/

[cwperks]

Opened a PR in core to address the maven snapshot publication issue: opensearch-project/OpenSearch#9149

[cwperks]

The CI checks can be re-run now

[codecov]

Codecov Report

Merging #456 (6b9cc27) into main (c2eef64) will not change coverage.
Report is 1 commits behind head on main.
The diff coverage is n/a.

@@            Coverage Diff            @@
##               main     #456   +/-   ##
=========================================
  Coverage     29.19%   29.19%           
  Complexity       98       98           
=========================================
  Files            22       22           
  Lines          1185     1185           
  Branches        109      109           
=========================================
  Hits            346      346           
  Misses          818      818           
  Partials         21       21