fix export pdf on metrics

[danangmassandy]

This is for #2078. A naive fix that adds margin height in the canvas.
Generated pdf:
Acinonyx jubatus jubatus - metrics (2).pdf

This fix will not work in data tab because the page is not fixed to 2. I've been trying another lib: https://ekoopmans.github.io/html2pdf.js/ that can support a page break. But the result is not that good either.
Data PDF using current implementation: Acinonyx jubatus jubatus,Loxodonta africana - reports.pdf.

• Text in row may be splitted
• Cannot control the page break

Data PDF using html2pdf.js: mydata.pdf.

• Random row height becomes higher
• Text in row is not splitted but row height is smaller.
• Spacing when using page break is not correct.

[github-actions]

☂️ Python Coverage

current status: ✅

Overall Coverage

Lines	Covered	Coverage	Threshold	Status
17061	16559	97%	0%	🟢

New Files

No new covered files...

Modified Files

No covered modified files...

updated for commit: b42afa3 by action🐍

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.26%. Comparing base (5ffb9a8) to head (b42afa3).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2095      +/-   ##
==========================================
- Coverage   97.26%   97.26%   -0.01%     
==========================================
  Files         375      375              
  Lines       16863    16863              
==========================================
- Hits        16402    16401       -1     
- Misses        461      462       +1     

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