BWC (rag processor): add version control for newly added request params

[pyek-bot]

Description

This change handles backward compatibility when upgrading from 2.12 to any version above it.
It has only been implemented upto 2.16 due to a certain divergence with the bedrock cohere support.
Eventually, it will be ported to 2.17 as well.

Related Issues

It is related to this issue #2983 and handles bwc from these 2 commits:

• Add support for Cohere and others. #2238
• Add request level parameters for system_prompt and user_instructions. #2236

Check List

• New functionality includes testing.
• New functionality has been documented.
• API changes companion pull request created.
• Commits are signed per the DCO using --signoff.
• Public documentation issue/PR created.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.
For more information on following Developer Certificate of Origin and signing off your commits, please check here.

[pyek-bot]

Please add backport label upto 2.13.

DO NOT merge backport PRs of this fix for 2.14 and 2.13 until the below change is merged and backported successfully:
#3123

[b4sjoo]

UT failed

[opensearch-trigger-bot]

The backport to 2.x failed:

The process '/usr/bin/git' failed with exit code 1

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add .worktrees/backport-2.x 2.x
# Navigate to the new working tree
cd .worktrees/backport-2.x
# Create a new branch
git switch --create backport/backport-3125-to-2.x
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 40c4e680e9ff9053b6f8ce718a31caca29c5e7d2
# Push it to GitHub
git push --set-upstream origin backport/backport-3125-to-2.x
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-2.x

Then, create a pull request where the base branch is 2.x and the compare/head branch is backport/backport-3125-to-2.x.

[opensearch-trigger-bot]

The backport to 2.16 failed:

The process '/usr/bin/git' failed with exit code 1

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add .worktrees/backport-2.16 2.16
# Navigate to the new working tree
cd .worktrees/backport-2.16
# Create a new branch
git switch --create backport/backport-3125-to-2.16
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 40c4e680e9ff9053b6f8ce718a31caca29c5e7d2
# Push it to GitHub
git push --set-upstream origin backport/backport-3125-to-2.16
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-2.16

Then, create a pull request where the base branch is 2.16 and the compare/head branch is backport/backport-3125-to-2.16.

[opensearch-trigger-bot]

The backport to 2.18 failed:

The process '/usr/bin/git' failed with exit code 1

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add .worktrees/backport-2.18 2.18
# Navigate to the new working tree
cd .worktrees/backport-2.18
# Create a new branch
git switch --create backport/backport-3125-to-2.18
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 40c4e680e9ff9053b6f8ce718a31caca29c5e7d2
# Push it to GitHub
git push --set-upstream origin backport/backport-3125-to-2.18
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-2.18

Then, create a pull request where the base branch is 2.18 and the compare/head branch is backport/backport-3125-to-2.18.