CobraDocs: Remove commit hash from docs. Fix issue with workdir replacement

[rohit-nayak-ps]

Description

• We remove the commit hash from the generated docs which resulted in unnecessary commits
• There was a failure in the sed command to replace <WORKDIR> due to incorrect sed invocation. Fixed here.
• There were files where the WORKDIR sed was not happening. Added

Related Issue(s)

There is a related website PR vitessio/website#1904 which will enhance the current make target to generate the docs to add modified content files to git with an appropriate git message including the current vitess hash.

We need to first merge this PR into main and then run make generated-docs in the website PR before it is ready.

Checklist

• "Backport to:" labels have been added if this change should be back-ported to release branches
• If this change is to be back-ported to previous releases, a justification is included in the PR description
• Tests were added or are not required
• Did the new or modified tests pass consistently locally and on CI?
• Documentation was added or is not required

Deployment Notes

[vitess-bot]

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[codecov]

Codecov Report

Attention: Patch coverage is 75.00000% with 3 lines in your changes missing coverage. Please review.

Project coverage is 67.53%. Comparing base (44aa9d7) to head (5b363ea).
Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
go/cmd/internal/docgen/docgen.go	75.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #17392      +/-   ##
==========================================
+ Coverage   67.47%   67.53%   +0.05%     
==========================================
  Files        1581     1581              
  Lines      253944   253956      +12     
==========================================
+ Hits       171353   171503     +150     
+ Misses      82591    82453     -138     

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