pgsql: meson: Add target for generating docs images

meson: Add target for generating docs images

This adds an 'images' target to the meson build system in order to
be able to regenerate the images used in the docs.

Author: Nazir Bilal Yavuz <byavuz81@gmail.com>
Reviewed-by: Daniel Gustafsson <daniel@yesql.se>
Reported-by: Daniel Gustafsson <daniel@yesql.se>
Discussion: /messages/by-id/CAN55FZ0c0Tcjx9=e-YibWGHa1-xmdV63p=THH4YYznz+pYcfig@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/4ec0e75afd488d41482ae10f6b5df9fa9a586dee

Modified Files
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doc/src/sgml/images/meson.build | 61 +++++++++++++++++++++++++++++++++++++++++
doc/src/sgml/meson.build | 2 ++
meson.build | 2 ++
3 files changed, 65 insertions(+)