[Backport 2.x] [Enhancement] Add schema validation and placeholders to index mappings

[opensearch-trigger-bot]

Backport 374cfd5 from #3240

[mingshl]

rerunning BWC 11

Run plugin_version=`./gradlew properties -q | grep "opensearch_build:" | awk '{print $2}'`

FAILURE: Build failed with an exception.

* Where:
Build file '/home/runner/work/ml-commons/ml-commons/ml-algorithms/build.gradle' line: 78

* What went wrong:
A problem occurred evaluating project ':opensearch-ml-algorithms'.
> Could not get unknown property 'versions' for object of type org.gradle.api.internal.artifacts.dsl.dependencies.DefaultDependencyHandler.

* Try:
> Run with --stacktrace option to get the stack trace.
> Run with --info or --debug option to get more log output.
> Run with --scan to get full insights.
> Get more help at https://help.gradle.org.

BUILD FAILED in [21](https://github.com/opensearch-project/ml-commons/actions/runs/12553722221/job/35001500146?pr=3310#step:4:22)s
plugin_version

Welcome to Gradle 8.11.1!

Here are the highlights of this release:
 - Parallel load and store for Configuration Cache
 - Java compilation errors at the end of the build output
 - Consolidated report for warnings and deprecations

For more details see https://docs.gradle.org/8.11.1/release-notes.html


[Incubating] Problems report is available at: file:///home/runner/work/ml-commons/ml-commons/build/reports/problems/problems-report.html
FAILURE: Build failed with an exception.

* Where:
Build file '/home/runner/work/ml-commons/ml-commons/ml-algorithms/build.gradle' line: 78

* What went wrong:
A problem occurred evaluating project ':opensearch-ml-algorithms'.
> Could not get unknown property 'versions' for object of type org.gradle.api.internal.artifacts.dsl.dependencies.DefaultDependencyHandler.

* Try:
> Run with --stacktrace option to get the stack trace.
> Run with --info or --debug option to get more log output.
> Run with --scan to get full insights.
> Get more help at https://help.gradle.org./


Deprecated Gradle features were used in this build, making it incompatible with Gradle 9.0.

You can use '--warning-mode all' to show the individual deprecation warnings and determine if they come from your own scripts or plugins.

For more on this, please refer to https://docs.gradle.org/8.11.1/userguide/command_line_interface.html#sec:command_line_warnings in the Gradle documentation.
BUILD FAILED in 1s
Error: Process completed with exit code 1.

[dhrubo-os]

rerunning BWC 11

Run plugin_version=`./gradlew properties -q | grep "opensearch_build:" | awk '{print $2}'`

FAILURE: Build failed with an exception.

* Where:
Build file '/home/runner/work/ml-commons/ml-commons/ml-algorithms/build.gradle' line: 78

* What went wrong:
A problem occurred evaluating project ':opensearch-ml-algorithms'.
> Could not get unknown property 'versions' for object of type org.gradle.api.internal.artifacts.dsl.dependencies.DefaultDependencyHandler.

* Try:
> Run with --stacktrace option to get the stack trace.
> Run with --info or --debug option to get more log output.
> Run with --scan to get full insights.
> Get more help at https://help.gradle.org.

BUILD FAILED in [21](https://github.com/opensearch-project/ml-commons/actions/runs/12553722221/job/35001500146?pr=3310#step:4:22)s
plugin_version

Welcome to Gradle 8.11.1!

Here are the highlights of this release:
 - Parallel load and store for Configuration Cache
 - Java compilation errors at the end of the build output
 - Consolidated report for warnings and deprecations

For more details see https://docs.gradle.org/8.11.1/release-notes.html


[Incubating] Problems report is available at: file:///home/runner/work/ml-commons/ml-commons/build/reports/problems/problems-report.html
FAILURE: Build failed with an exception.

* Where:
Build file '/home/runner/work/ml-commons/ml-commons/ml-algorithms/build.gradle' line: 78

* What went wrong:
A problem occurred evaluating project ':opensearch-ml-algorithms'.
> Could not get unknown property 'versions' for object of type org.gradle.api.internal.artifacts.dsl.dependencies.DefaultDependencyHandler.

* Try:
> Run with --stacktrace option to get the stack trace.
> Run with --info or --debug option to get more log output.
> Run with --scan to get full insights.
> Get more help at https://help.gradle.org./


Deprecated Gradle features were used in this build, making it incompatible with Gradle 9.0.

You can use '--warning-mode all' to show the individual deprecation warnings and determine if they come from your own scripts or plugins.

For more on this, please refer to https://docs.gradle.org/8.11.1/userguide/command_line_interface.html#sec:command_line_warnings in the Gradle documentation.
BUILD FAILED in 1s
Error: Process completed with exit code 1.

@pyek-bot you need to add some code from this PR : https://github.com/opensearch-project/ml-commons/pull/2800/files

In 2.x branch we don't have versions variable available.

[pyek-bot]

@dhrubo-os should we add backport label to this pr instead of making changes in mine

Edit: nvm, the pr mentions why it was not backported to 2.x, i will manually introduced versions variable

[pyek-bot]

Raised a manual backport PR with the required changes: #3342