[DOCS] Adds getting started content based on the template

[szabosteve]

Overview

This PR adds a getting started page to the .NET client documentation. The content is based on the client getting started template.

For the reviewer co-author

Please provide content/example code for the following sections:

• Requirements
• Installation
• Connecting
• Creating an index
• Indexing documents
• Getting documents
• Searching documents
• Updating documents
• Deleting documents
• Deleting an index

Preview

Getting started

[szabosteve]

@elasticmachine test this please

[github-actions]

The backport to 8.8 failed:

The process '/usr/bin/git' failed with exit code 128

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-8.8 8.8
# Navigate to the new working tree
cd .worktrees/backport-8.8
# Create a new branch
git switch --create backport-7764-to-8.8
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick --mainline 1 ff63b789acaa244a2ce387d0de7ab91562e0cfa6
# Push it to GitHub
git push --set-upstream origin backport-7764-to-8.8
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-8.8

Then, create a pull request where the base branch is 8.8 and the compare/head branch is backport-7764-to-8.8.

[github-actions]

The backport to 8.9 failed:

The process '/usr/bin/git' failed with exit code 128

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-8.9 8.9
# Navigate to the new working tree
cd .worktrees/backport-8.9
# Create a new branch
git switch --create backport-7764-to-8.9
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick --mainline 1 ff63b789acaa244a2ce387d0de7ab91562e0cfa6
# Push it to GitHub
git push --set-upstream origin backport-7764-to-8.9
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-8.9

Then, create a pull request where the base branch is 8.9 and the compare/head branch is backport-7764-to-8.9.