Add misc improvements to the framework

[swallez]

This PR adds a number of improvements and bugfixes to the JSON and utility classes:

JSON framework:

• A new BufferingJsonpMapper allows the creation of JsonGenerator that store JSON events in a buffer that can be replayed. This is useful to efficiently create synthetic JSON documents.
• An additional JsonpMapper.deserialize method variant accepts the current JSON event. Fixes GetSource API throws TransportException #741
• The Jackson implementation of JsonpMapper now enables the ACCEPT_SINGLE_VALUE_AS_ARRAY deserialization feature. This allows single values in a JSON stream to be considered as a single-value collection.

API & transport framework:

• ElasticsearchException now holds the low level http response, so that the application can inspect the details of the error.
• Endpoints now have a call methods, to make calling endpoints programmatically easier. This is for advanced use, as an applicaition will normally use the ElasticsearchClient that hides endpoint objects.
• A BinaryDataResponse can now easily be created from a byte array.

Test framework:

• The ElasticsearchTestServer now tries to contact an Elasticsearch server running on http://elastic:changeme@localhost:9200 before spawning a container.
• A MockHttpClient has been added that allows writing integration-like tests without requiring a running server. This is an alternative to using com.sun.net.httpserver.HttpServer when we want to rest http response decoding but don't need to test the network layer.

[github-actions]

The backport to 7.17 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-7.17 7.17
# Navigate to the new working tree
cd .worktrees/backport-7.17
# Create a new branch
git switch --create backport-760-to-7.17
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick --mainline 1 b5aed69e3311caef0090fc616b5628fb269e1e34
# Push it to GitHub
git push --set-upstream origin backport-760-to-7.17
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-7.17

Then, create a pull request where the base branch is 7.17 and the compare/head branch is backport-760-to-7.17.