feat: support show variables and set variable

[jingchen2222]

• Please check if the PR fulfills these requirements

• The commit message follows our guidelines
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

• What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)
  feature

• What is the current behavior? (You can also link to an open issue here)
  resolve SQL: support set and show session system variable and global system variable syntax and logical plan #863

• What is the new behavior (if this is a feature change)?

• Does this PR introduce a breaking change? (What changes might users need to make in their application due to this PR?)

• Other information:

[github-actions]

Linux Test Report

       60 files       180 suites   35m 10s ⏱️
  9 197 tests   9 197 ✔️ 0 💤 0 ❌
13 269 runs  13 269 ✔️ 0 💤 0 ❌

Results for commit 9b48416.

♻️ This comment has been updated with latest results.

[github-actions]

HybridSE Linux Test Report

       71 files       237 suites   5m 24s ⏱️
18 990 tests 18 990 ✔️ 0 💤 0 ❌
19 021 runs  19 021 ✔️ 0 💤 0 ❌

Results for commit 9b48416.

♻️ This comment has been updated with latest results.

[github-actions]

HybridSE Mac Test Report

       71 files       237 suites   6m 25s ⏱️
18 990 tests 18 990 ✔️ 0 💤 0 ❌
19 021 runs  19 021 ✔️ 0 💤 0 ❌

Results for commit 9b48416.

♻️ This comment has been updated with latest results.

[codecov]

Codecov Report

Merging #892 (9b48416) into main (63b4a43) will increase coverage by 0.01%.
The diff coverage is 98.30%.

@@             Coverage Diff              @@
##               main     #892      +/-   ##
============================================
+ Coverage     83.07%   83.08%   +0.01%     
  Complexity       22       22              
============================================
  Files           283      283              
  Lines         52981    53025      +44     
  Branches         31       31              
============================================
+ Hits          44013    44055      +42     
- Misses         8959     8961       +2     
  Partials          9        9              

Impacted Files	Coverage Δ
hybridse/include/node/node_manager.h	100.00% <ø> (ø)
hybridse/include/node/sql_node.h	72.34% <92.85%> (+0.19%)	⬆️
hybridse/include/node/plan_node.h	84.33% <100.00%> (+0.07%)	⬆️
hybridse/include/sdk/result_set.h	88.23% <100.00%> (ø)
hybridse/src/node/node_manager.cc	88.57% <100.00%> (ø)
hybridse/src/node/plan_node.cc	84.81% <100.00%> (+0.05%)	⬆️
hybridse/src/node/sql_node.cc	78.48% <100.00%> (-0.04%)	⬇️
hybridse/src/planv2/ast_node_converter.cc	94.05% <100.00%> (+0.10%)	⬆️
hybridse/src/planv2/ast_node_converter_test.cc	95.75% <100.00%> (+0.03%)	⬆️
hybridse/src/planv2/planner_v2_test.cc	96.26% <100.00%> (ø)
... and 1 more

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[aceforeverd]

LGTM

[jingchen2222]

Reorganize OpenMLDB modes 0.4.0 related work