Reformat docs and add a new CLI option

[rubo]

Changes

• Updated the configuration and metrics docs to provide a link for each configuration/metrics option
• Added "CLI | Environment variable | Configuration file" section to each configuration option
• Revised links
• Added DB size source directory CLI option for DB size generator

Types of changes

What types of changes does your code introduce?

• Bugfix (a non-breaking change that fixes an issue)
• New feature (a non-breaking change that adds functionality)
• Breaking change (a change that causes existing functionality not to work as expected)
• Optimization
• Refactoring
• Documentation update
• Build-related changes
• Other: Description

Testing

Requires testing

• Yes
• No

Documentation

Requires documentation update

• Yes
• No

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