Docs: add light syntax highlighting theme

[huynhicode]

📑 Summary

This PR adds light syntax highlighting to the code block theme. No changes to dark mode.

See screenshots:

Resolves #4971

📏 Design Decisions

n/a

📋 Tasks

Make sure you

• 📖 have read the contribution guidelines
• 💻 have added necessary unit/e2e tests.
• 📓 have added documentation. Make sure MERMAID_RELEASE_VERSION is used for all new features.
• 🔖 targeted develop branch

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[codecov]

Codecov Report

Merging #4998 (dc2373e) into master (f1895ac) will increase coverage by 1.10%.
Report is 345 commits behind head on master.
The diff coverage is 75.02%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4998      +/-   ##
==========================================
+ Coverage   76.03%   77.14%   +1.10%     
==========================================
  Files         146      164      +18     
  Lines       14569    13820     -749     
  Branches      592      693     +101     
==========================================
- Hits        11078    10661     -417     
+ Misses       3368     3003     -365     
- Partials      123      156      +33     

Flag	Coverage Δ
e2e	82.45% <86.42%> (-0.11%)	⬇️
unit	42.94% <25.39%> (-2.62%)	⬇️

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

Files	Coverage Δ
packages/mermaid/src/config.ts	68.82% <100.00%> (-5.67%)	⬇️
packages/mermaid/src/dagre-wrapper/clusters.js	87.25% <ø> (-0.99%)	⬇️
packages/mermaid/src/dagre-wrapper/createLabel.js	92.85% <ø> (ø)
packages/mermaid/src/dagre-wrapper/index.js	98.82% <100.00%> (ø)
packages/mermaid/src/dagre-wrapper/markers.js	100.00% <100.00%> (ø)
...ages/mermaid/src/dagre-wrapper/mermaid-graphlib.js	90.95% <100.00%> (ø)
packages/mermaid/src/dagre-wrapper/nodes.js	78.36% <100.00%> (-11.26%)	⬇️
packages/mermaid/src/dagre-wrapper/shapes/note.js	100.00% <ø> (ø)
packages/mermaid/src/dagre-wrapper/shapes/util.js	96.22% <ø> (ø)
packages/mermaid/src/defaultConfig.ts	47.98% <100.00%> (+0.77%)	⬆️
... and 73 more

... and 26 files with indirect coverage changes

[huynhicode]

Looks like a similar PR was submitted on Oct 7th by a community member.

PR-4924 to resolve issue 4905

Closing my PR as it is a duplicate and was submitted after 4924.