Made fast_import more testable and changed dbname to neondb

[NanoBjorn]

Problem

postgres is system database at neon, so we need to do pg_restore into neondb instead

https://github.com/neondatabase/cloud/issues/22100

Summary of changes

Changed fast_import a little bit:

1. After succesfull connection creating neondb in postgres instance
2. Changed restore connstring to use new db
3. Added optional source_connection_string, which allows to skip s3_prefix and just connect directly.
4. Added -i that stops process until sigterm

TODO

• test image in cplane e2e
• Change import job image back to latest after this merged (partial revert of https://github.com/neondatabase/cloud/pull/22338)

[github-actions]

7095 tests run: 6797 passed, 0 failed, 298 skipped (full report)

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Flaky tests (3)

Postgres 17

• test_timeline_archival_chaos: release-x86-64, release-arm64

Postgres 16

• test_physical_replication_config_mismatch_too_many_known_xids: release-arm64

Code coverage* (full report)

• functions: 31.3% (8405 of 26882 functions)
• lines: 47.9% (66697 of 139109 lines)

* collected from Rust tests only

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_{The comment gets automatically updated with the latest test results
73c14a7 at 2025-01-02T15:01:46.637Z :recycle:}