Add higher-level HTTP DSL methods

[Xtansia]

Description

Adds the higher-level HTTP DSL methods to wrap DoRequest and allow better ergonomics.

Issues Resolved

Closes #403

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[dblock]

Why do we need .LowLevel at all?

[dblock]

Thanks for fixing this :)

[dblock]

I would remove client.LowLevel from the documentation. There's no reason to use that.

[Xtansia]

Why do we need .LowLevel at all?

All requests are eventually handled via .LowLevel/OpenSearch.Net. However in future it'd be ideal to simplify and only have a single client package keeping just the transport layer separate, similar to what NEST did in v8.

[dblock]

Looks OK. I think I'd remove any mention of LowLevel from the documentation and samples. In my opinion writing client.Http.GetAsync is 100x better.

[Xtansia]

Converting to draft as there's some naming conventions that need fixing or excluding from conventions tests

[Xtansia]

Only failing test now, is a known flakey test

[dblock]

Retry tests till they pass? 😢

[opensearch-trigger-bot]

The backport to 1.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-1.x 1.x
# Navigate to the new working tree
cd .worktrees/backport-1.x
# Create a new branch
git switch --create backport/backport-447-to-1.x
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 9054705954d5f763ed6a8707dc8c925ec4b2e3a8
# Push it to GitHub
git push --set-upstream origin backport/backport-447-to-1.x
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-1.x

Then, create a pull request where the base branch is 1.x and the compare/head branch is backport/backport-447-to-1.x.