feat: expose wal config

[v0y4g3r]

I hereby agree to the terms of the GreptimeDB CLA

What's changed and what's your intention?

• Allow users to config wal parameters thru config files.

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 #852 (2d3e108) into develop (fa54870) will increase coverage by 0.25%.
The diff coverage is 92.25%.

@@             Coverage Diff             @@
##           develop     #852      +/-   ##
===========================================
+ Coverage    86.06%   86.32%   +0.25%     
===========================================
  Files          420      419       -1     
  Lines        55107    55027      -80     
===========================================
+ Hits         47429    47500      +71     
+ Misses        7678     7527     -151     

Flag	Coverage Δ
rust	86.32% <92.25%> (+0.25%)	⬆️

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

Impacted Files	Coverage Δ
src/common/base/src/lib.rs	100.00% <ø> (ø)
src/cmd/src/standalone.rs	56.30% <50.00%> (ø)
src/cmd/src/datanode.rs	78.23% <85.71%> (+0.76%)	⬆️
src/common/base/src/readable_size.rs	91.11% <91.11%> (ø)
src/datanode/src/datanode.rs	58.18% <100.00%> (+10.45%)	⬆️
src/datanode/src/instance.rs	53.33% <100.00%> (-16.67%)	⬇️
src/datanode/src/mock.rs	100.00% <100.00%> (ø)
src/frontend/src/tests.rs	95.62% <100.00%> (+1.27%)	⬆️
src/log-store/src/config.rs	100.00% <100.00%> (ø)
src/log-store/src/raft_engine/log_store.rs	88.86% <100.00%> (ø)
... and 54 more

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[fengjiachun]

LGTM