Update readme and more GitHub pages setup

[kolchfa-aws]

Description

This PR:

• Includes the contributing.md file to be built as a webpage
• Adds the hosted documentation link to the readme
• Adds favicon

Issues Resolved

N/A

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[owaiskazi19]

@kolchfa-aws can we have favicon.ico under assets?
I also think _includes and _layouts should be under assets at one place. We should not have new directories under root unless it define a new section of the code. This is mostly part of documentation website so can be pulled in one directory.

[kolchfa-aws]

Moved favicon. I don't think I can move any of the other files as Jekyll expects them to be there in the root directory. There is an option to publish off of a dedicated branch though. We'll just have to make sure that any changes to documentation are automatically merged into that branch.

[opensearch-trigger-bot]

The backport to 1.x failed:

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

To backport manually, run these commands in your terminal:

# Navigate to the root of your repository
cd $(git rev-parse --show-toplevel)
# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add ../.worktrees/opensearch-sdk-java/backport-1.x 1.x
# Navigate to the new working tree
pushd ../.worktrees/opensearch-sdk-java/backport-1.x
# Create a new branch
git switch --create backport/backport-869-to-1.x
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 a89872744d2a653139f522b08e3ff1e0e8f78f4f
# Push it to GitHub
git push --set-upstream origin backport/backport-869-to-1.x
# Go back to the original working tree
popd
# Delete the working tree
git worktree remove ../.worktrees/opensearch-sdk-java/backport-1.x

Then, create a pull request where the base branch is 1.x and the compare/head branch is backport/backport-869-to-1.x.