feat: update mysql default listen port to 4406

[azhsmesos]

Signed-off-by: azhmesoso zzhncut123@163.com
I hereby agree to the terms of the GreptimeDB CLA

What's changed and what's your intention?

Right now the datanode listens on 127.0.0.1:3306 for MySQL connections, it may conflict with the user's MySQL server, so I should change this default address to 127.0.0.1:4406.
Please explain IN DETAIL what the changes are in this PR and why they are needed:

• Summarize your change (mandatory)
  updata mysql default listen port to 4406.
• How does this PR work? Need a brief introduction for the changed logic (optional)
• Describe clearly one logical change and avoid lazy messages (optional)
• Describe any limitations of the current code (optional)

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)

[azhsmesos]

@waynexia please review it for me, thanks.

[codecov]

Codecov Report

Merging #568 (594fd51) into develop (f878827) will decrease coverage by 0.00%.
The diff coverage is 66.66%.

@@             Coverage Diff             @@
##           develop     #568      +/-   ##
===========================================
- Coverage    86.35%   86.35%   -0.01%     
===========================================
  Files          398      398              
  Lines        50165    50165              
===========================================
- Hits         43322    43321       -1     
- Misses        6843     6844       +1     

Flag	Coverage Δ
rust	86.35% <66.66%> (-0.01%)	⬇️

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

Impacted Files	Coverage Δ
src/cmd/src/standalone.rs	37.35% <0.00%> (ø)
src/cmd/src/datanode.rs	81.69% <100.00%> (ø)
src/datanode/src/datanode.rs	52.63% <100.00%> (ø)
src/meta-srv/src/service/heartbeat.rs	86.31% <0.00%> (-1.06%)	⬇️

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[paomian]

It should be better to modify the default mysql port in datanode.rs.
By the way, there are some test about datanode default mysql port config in datanode.example.toml

[azhsmesos]

It should be better to modify the default mysql port in datanode.rs. By the way, there are some test about datanode default mysql port config in datanode.example.toml

I have a question, what's the difference between mysql_addr = '127.0.0.1:4406' and datanode_mysql_addr = '127.0.0.1:4406'

[paomian]

datanode_mysql_addr purpose is just for testing.
It's used when start in distribution mode. In the future, we will make it optional.

[killme2008]

LGTM

[v0y4g3r]

LGTM