[Docs] Omit "$" character when copying code

[seonWKim]

Motivation:

When copying code from documentation, "$" is copied. It's painful to copy code with "$" because users will have to delete the it everytime.

Modifications:

• Omit the "$" when it's a prefix

Result:

• Closes #https://github.com/line/armeria/issues/5322. (If this resolves the issue.)
• Code is copied without "$" prefix

[github-actions[bot]]

🔍 Build Scan® (commit: e1d995be6dddfda5d7c761fe7db2cf3523c02ba6)

Job name	Status	Build Scan®
build-windows-latest-jdk-19	✅	https://ge.armeria.dev/s/2f6opotcmgvec
build-self-hosted-jdk-8	❌ (failure)	https://ge.armeria.dev/s/iy3nnodzq32re
build-self-hosted-jdk-19-snapshot-blockhound	✅	https://ge.armeria.dev/s/dmzmhdha7o4ts
build-self-hosted-jdk-17-min-java-17-coverage	✅	https://ge.armeria.dev/s/zk26k53v2ugsi
build-self-hosted-jdk-17-min-java-11	✅	https://ge.armeria.dev/s/lgdr6g4o6ii2m
build-self-hosted-jdk-17-leak	✅	https://ge.armeria.dev/s/ekvcpoqoytopm
build-self-hosted-jdk-11	✅	https://ge.armeria.dev/s/knbfljwrlt25y
build-macos-12-jdk-19	✅	https://ge.armeria.dev/s/zihmryy3ddtoy

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 73.94%. Comparing base (6a5f3ad) to head (01468ec). Report is 206 commits behind head on main.

:exclamation: Current head 01468ec differs from pull request most recent head e1d995b. Consider uploading reports for the commit e1d995b to get more accurate results

Additional details and impacted files

@@            Coverage Diff            @@
##               main    #5334   +/-   ##
=========================================
  Coverage     73.93%   73.94%           
- Complexity    20098    20099    +1     
=========================================
  Files          1730     1730           
  Lines         74142    74142           
  Branches       9461     9461           
=========================================
+ Hits          54815    54822    +7     
+ Misses        14852    14845    -7     
  Partials       4475     4475           

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