Remove all PostgreSQL compatibility documentation and references

[Copilot]

The PostgreSQL compatibility layer documentation was removed in a previous commit, but numerous references remained throughout the documentation causing broken links in the build.

Changes

Removed PostgreSQL references from:

• Developer getting started guides (EN/RU) - API options, driver installation, coding sections
• Reference documentation index (EN/RU) - PostgreSQL compatibility section
• Integration documentation (EN/RU) - PostgreSQL wire protocol mentions
• TLS configuration (EN/RU) - PostgreSQL wire protocol configuration section
• Data-in-transit encryption (EN/RU) - PostgreSQL protocol from supported protocols list
• Changelog files (EN/RU) - PostgreSQL-related CLI commands, features, and announcements
• CLI commands reference (RU) - tools pg-convert command

Deleted files:

• ydb/docs/en/core/integrations/visualization/finebi.md - FineBI integration via PostgreSQL
• ydb/docs/ru/core/integrations/visualization/finebi.md - Russian version
• Updated visualization compatibility tables to remove FineBI entries

Updated index files:

• Removed PostgreSQL compatibility links from main documentation indexes (EN/RU)
• Updated integration notes to reference only Kafka compatibility layer

Total: 23 files changed, 394 deletions removed

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