Add praefect prometheus_exclude_database_from_default_metrics config value

What does this MR do?

Praefect has a new configuration value to control whether or not it will hit the database for metrics. This change adds the prometheus_exclude_database_from_default_metrics config value and writes it into the right place in the praefect config toml.

corresponding gitaly MR is gitaly!4085 (merged)

Related issues

Checklist

See Definition of done.

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Required

• Merge Request Title, and Description are up to date, accurate, and descriptive
• MR targeting the appropriate branch
• MR has a green pipeline on GitLab.com
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Expected (please provide an explanation if not completing)

• Test plan indicating conditions for success has been posted and passes
• Documentation created/updated
• Tests added
• Integration tests added to GitLab QA
• Equivalent MR/issue for the GitLab Chart opened