Document JetStream installation and manual configuration

[welteki]

Description

Introduce terminology required to understand JetStream and document the installation process.

Explain limits and document manual Stream and Consumer creation for users that need higher limits than the defaults.

Motivation and Context

• [ ] I have raised an issue to propose this change (required)

Improve JetStream documentation for users who need higher limits than the defaults.

How Has This Been Tested?

Ran docs site locally to verify.

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• [x] My code follows the code style of this project.
• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.
• [x] I've read the CONTRIBUTION guide
• [x] I have signed-off my commits with git commit -s