Implement DropDatabase and Status

[chilagrow]

Description

Closes #3404.

Readiness checklist

• I added/updated unit tests (and they pass).
• I added/updated integration/compatibility tests (and they pass).
• I added/updated comments and checked rendering.
• I made spot refactorings.
• I updated user documentation.
• I ran task all, and it passed.
• I ensured that PR title is good enough for the changelog.
• (for maintainers only) I set Reviewers (@FerretDB/core), Milestone (Next), Labels, Project and project's Sprint fields.
• I marked all done items in this checklist.

[codecov]

Codecov Report

Merging #3451 (2aff1da) into main (7efc265) will decrease coverage by 2.10%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##             main    #3451      +/-   ##
==========================================
- Coverage   75.38%   73.28%   -2.10%     
==========================================
  Files         422      422              
  Lines       26263    26296      +33     
==========================================
- Hits        19798    19272     -526     
- Misses       5322     5845     +523     
- Partials     1143     1179      +36     

Files	Coverage Δ
internal/backends/postgresql/backend.go	10.71% <0.00%> (-50.08%)	⬇️

... and 46 files with indirect coverage changes

Flag	Coverage Δ
filter-true	68.57% <0.00%> (-3.48%)	⬇️
hana-1	?
integration	68.57% <0.00%> (-3.48%)	⬇️
mongodb-1	4.64% <0.00%> (-0.01%)	⬇️
pg-1	41.35% <0.00%> (-0.02%)	⬇️
pg-2	42.42% <0.00%> (+0.04%)	⬆️
pg-3	?
postgresql-1	∅ <ø> (∅)
postgresql-2	?
postgresql-3	?
sort-false	68.57% <0.00%> (-3.48%)	⬇️
sqlite-1	40.36% <0.00%> (-0.03%)	⬇️
sqlite-2	41.62% <0.00%> (-0.05%)	⬇️
sqlite-3	43.21% <0.00%> (-0.06%)	⬇️
unit	24.48% <0.00%> (-0.06%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

[chilagrow]

Once #3406 is merged, integration tests would pass.

$ task test-integration-postgresql TEST_RUN='TestCommandsAdministrationCreateDropListDatabases|TestPingCommand|TestCommandsAdministrationServerStatus'
task: [test-integration-postgresql] go test -count=1 -run='TestCommandsAdministrationCreateDropListDatabases|TestPingCommand|TestCommandsAdministrationServerStatus' -timeout=35m -race=true -tags=ferretdb_debug,ferretdb_hana -shuffle=on -coverpkg=../... -coverprofile=integration-postgresql.txt -target-backend=ferretdb-pg -target-tls -postgresql-url='postgres://username@127.0.0.1:5432/ferretdb?pool_max_conns=50&search_path=' -compat-url='mongodb://username:password@127.0.0.1:47018/?tls=true&tlsCertificateKeyFile=../build/certs/client.pem&tlsCaFile=../build/certs/rootCA-cert.pem' -use-new-pg -disable-filter-pushdown=false -enable-sort-pushdown=false

2023-09-28T14:43:08.673+0900    INFO    setup/startup.go:94     Target system: ferretdb-pg (built-in).
2023-09-28T14:43:08.674+0900    INFO    debug   debug/debug.go:92       Starting debug server on http://127.0.0.1:45535/
2023-09-28T14:43:08.806+0900    INFO    setup/startup.go:105    Compat system: MongoDB (mongodb://username:password@127.0.0.1:47018/?tls=true&tlsCertificateKeyFile=../build/certs/client.pem&tlsCaFile=../build/certs/rootCA-cert.pem).
-test.shuffle 1695879788806711384
PASS
coverage: 16.5% of statements in ../...
ok      github.com/FerretDB/FerretDB/integration        24.164s

[AlekSi]

#3451 (comment)

[rumyantseva]

LGTM