feat: add dockerfile for docs ci

[purelind]

add dockerfile for docs ci

[ti-chi-bot[bot]]

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[ti-chi-bot[bot]]

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[purelind]

When using the new image built with this new dockerfile for PDF generation, the following errors may occur.

scripts/generate_pdf.sh

[pandoc warning] Could not find image `/media/ticdc/ticdc-architecture-3.PNG', skipping...
! Missing number, treated as zero.
<to be read again>
                   \protect
l.214982 ...r}\rule{0.5\linewidth}{\linethickness}

pandoc: Error producing PDF

related to this script https://github.com/pingcap/docs/blob/master/scripts/generate_pdf.sh

[purelind]

LaTeX Warning: No \author given.

! LaTeX Error: Unicode character ɪ (U+026A)
               not set up for use with LaTeX.

See the LaTeX manual or LaTeX Companion for explanation.
Type  H <return>  for immediate help.
 ...

l.120 ...://github.com/pingcap/tidb}{TiDB} (/'taɪ
                                                  diːbi:/, ``Ti''