fix: skip linking database if password is missing

[sweatybridge]

What kind of change does this PR introduce?

Relates to #4419

What is the new behavior?

• Skips linking database if password is omitted.
• Prefer direct connection if user supports IPv6.
• Simplifies linking by not setting up migrations table.
• Unban pooler IP address together with local IP.
• Print better suggestions on missing database password.

Additional context

Add any other context or screenshots.

[snyk-io]

✅ Snyk checks have passed. No issues have been found so far.

Status	Scanner	Critical	High	Medium	Low	Total (0)
✅	Code Security	0	0	0	0	0 issues

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[coveralls]

Pull Request Test Coverage Report for Build 19288913427

Details

• 33 of 92 (35.87%) changed or added relevant lines in 6 files are covered.
• 29 unchanged lines in 6 files lost coverage.
• Overall coverage decreased (-0.3%) to 54.407%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
internal/branches/get/get.go	0	1	0.0%
internal/link/link.go	6	7	85.71%
internal/bootstrap/bootstrap.go	0	4	0.0%
internal/bans/get/get.go	0	5	0.0%
internal/utils/connect.go	6	13	46.15%
internal/utils/flags/db_url.go	21	62	33.87%

Files with Coverage Reduction	New Missed Lines	%
internal/bans/get/get.go	1	0.0%
internal/utils/api.go	2	87.63%
internal/utils/connect.go	3	89.04%
internal/gen/keys/keys.go	5	12.9%
internal/link/link.go	9	73.8%
internal/utils/flags/db_url.go	9	42.13%

Totals
Change from base Build 19286434813:	-0.3%
Covered Lines:	6358
Relevant Lines:	11686

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💛 - Coveralls