feat: disable mysql server on datande when running standalone mode

[v0y4g3r]

I hereby agree to the terms of the GreptimeDB CLA

What's changed and what's your intention?

Disable mysql server on datande when running standalone mode

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)

Fixes #556

[codecov]

Codecov Report

Merging #593 (f7f6495) into develop (c94b544) will decrease coverage by 0.01%.
The diff coverage is 3.70%.

@@             Coverage Diff             @@
##           develop     #593      +/-   ##
===========================================
- Coverage    86.47%   86.45%   -0.02%     
===========================================
  Files          399      399              
  Lines        50640    50649       +9     
===========================================
- Hits         43790    43789       -1     
- Misses        6850     6860      +10     

Flag	Coverage Δ
rust	86.45% <3.70%> (-0.02%)	⬇️

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

Impacted Files	Coverage Δ
src/cmd/src/datanode.rs	81.69% <ø> (ø)
src/cmd/src/frontend.rs	65.51% <ø> (ø)
src/cmd/src/standalone.rs	37.35% <ø> (ø)
src/datanode/src/datanode.rs	52.63% <ø> (ø)
src/datanode/src/instance.rs	35.07% <ø> (ø)
src/datanode/src/server.rs	0.00% <0.00%> (ø)
src/frontend/src/frontend.rs	48.57% <ø> (-1.43%)	⬇️
src/frontend/src/instance.rs	73.31% <ø> (ø)
src/frontend/src/instance/influxdb.rs	0.00% <ø> (ø)
src/frontend/src/instance/opentsdb.rs	91.20% <ø> (ø)
... and 6 more

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[killme2008]

Good job, but we have to remove the MySQL options in StandaloneOptions too. https://github.com/GreptimeTeam/greptimedb/blob/develop/src/cmd/src/standalone.rs#L73-L74

[killme2008]

LGTM