feat(plugins): support text COPY

[levkk]

Add support for routing COPY rows using plugins. Currently only COPY ... FORMAT text|csv is supported. Will add binary as a follow-up, it requires adding some helpers to parse the format to the plugin crate.

[codecov]

Codecov Report

❌ Patch coverage is 51.39665% with 87 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
pgdog-plugin/src/copy.rs	44.44%	55 Missing ⚠️
pgdog/src/frontend/router/parser/copy.rs	64.00%	18 Missing ⚠️
pgdog-plugin/src/plugin.rs	0.00%	12 Missing ⚠️
pgdog-macros/src/lib.rs	88.88%	2 Missing ⚠️

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