Remove all end-user documentation from Data Prepper repo

[dlvenable]

Currently, Data Prepper has end-user documentation in plugin repos and the docs folder. Much of this information is already in the opensearch.org documentation Git repo and thus is duplicated.

Update all plugin README.md files to have the following structure:

# plugin_name

<Brief introduction>

<Link to the opensearch.org documentation>

## Developer guide

<Any specific instructions for developing within this plugin>

Also, update the end-user documentation in the docs directory to simply redirect users to the opensearch.org documentation.

# Original title

This documentation has moved to <link to the opensearch.org documentation>.

Tasks

• Collect the plugins that need to be added and put below.

Plugins

• s3-source

Docs directory