MongoDB: compatibility with >=mongo-cpp-driver-4

[parona-source]

What does this PR do?

Fix api incompatibilities with >=mongo-cpp-driver-4.

https://www.mongodb.com/docs/languages/cpp/cpp-driver/current/upgrade/#api-breaking-changes-in-v4.0

k_string is available as far back as 3.7, but I think its simpler to just check if the version is higher than 4.

What are related issues/pull requests?

Tasklist

• AI (Copilot or something similar) supported my development of this PR
• Make sure code is correctly formatted (cf pre-commit configuration)
• Add test case(s)
• Add documentation
• Updated Python API documentation (swig/include/python/docs/)
• Review
• Adjust for comments
• All CI builds and checks have passed
• ADD YOUR TASKS HERE

Environment

Provide environment details, if relevant:

• OS: Gentoo Linux amd64
• Compiler: gcc (Gentoo 15.1.1_p20250705-r1 p2) 15.1.1 20250705

[rouault]

@parona-source Would you mind bumping MONGO_C_DRIVER_VERSION and MONGOCXX_VERSION in .github/workflows/ubuntu_24.04/Dockerfile.ci so that continuous integration can test this ?

[rouault]

The backport to release/3.11 failed:

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

stderr

To https://github.com/OSGeo/gdal.git
 ! [remote rejected]       backport-12837-to-release/3.11 -> backport-12837-to-release/3.11 (refusing to allow a Personal Access Token to create or update workflow `.github/workflows/ubuntu_24.04/Dockerfile.ci` without `workflow` scope)
error: failed to push some refs to 'https://github.com/OSGeo/gdal.git'

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-release/3.11 release/3.11
# Navigate to the new working tree
cd .worktrees/backport-release/3.11
# Create a new branch
git switch --create backport-12837-to-release/3.11
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick 001e2abd31cbd3489891de7c3b403cecac3c8c0d,b3b77bdc132590a535d3438e8a136da100d7cc77
# Push it to GitHub
git push --set-upstream origin backport-12837-to-release/3.11
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-release/3.11

Then, create a pull request where the base branch is release/3.11 and the compare/head branch is backport-12837-to-release/3.11.

[rouault]

manually cherry-picked to 3.11 per 7c04261 and c855118