refactor: make postgres handler stateful

[sunng87]

I hereby agree to the terms of the GreptimeDB CLA

What's changed and what's your intention?

This patch updates pgwire to 0.8 and make our PostgresServerHandler stateful (one handler per connection). This is prerequisite for upcoming prepared statement support.

Checklist

• I have written the necessary rustdoc comments.
• I have added the necessary unit tests and integration tests.

Refer to a related PR or issue link (optional)

[codecov]

Codecov Report

Merging #914 (be57c13) into develop (a7dc86f) will decrease coverage by 0.15%.
The diff coverage is 73.62%.

@@             Coverage Diff             @@
##           develop     #914      +/-   ##
===========================================
- Coverage    86.19%   86.04%   -0.15%     
===========================================
  Files          430      431       +1     
  Lines        58227    58246      +19     
===========================================
- Hits         50187    50118      -69     
- Misses        8040     8128      +88     

Flag	Coverage Δ
rust	86.04% <73.62%> (-0.15%)	⬇️

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

Impacted Files	Coverage Δ
src/servers/src/postgres/handler.rs	83.21% <14.81%> (-7.46%)	⬇️
src/servers/src/postgres/auth_handler.rs	88.48% <95.00%> (-1.46%)	⬇️
src/servers/src/postgres.rs	100.00% <100.00%> (ø)
src/servers/src/postgres/server.rs	96.92% <100.00%> (-0.10%)	⬇️
src/object-store/src/test_util.rs	0.00% <0.00%> (-100.00%)	⬇️
src/datanode/src/instance.rs	47.11% <0.00%> (-10.67%)	⬇️
tests-integration/src/test_util.rs	79.18% <0.00%> (-9.39%)	⬇️
src/servers/src/error.rs	38.59% <0.00%> (-5.27%)	⬇️
src/servers/src/opentsdb.rs	96.82% <0.00%> (-1.59%)	⬇️
src/meta-srv/src/service/heartbeat.rs	86.17% <0.00%> (-1.07%)	⬇️
... and 4 more

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[shuiyisong]

LGTM