Fix hardcoded HTML docs installation destination

The patch fixes hardcoded (share/doc) installation location for HTML
documents in 2.3.1 version. The problem[1] apparently has recently been
fixed in master[2], but not backported to 2.3 branch.

References:
[1] uclouvain/openjpeg#1322
[2] uclouvain/openjpeg@aaddbc7

openjpeg-2.3.1.diff

@@ -0,0 +1,15 @@
+# Fix hardcoded docs destination
+# See https://github.com/uclouvain/openjpeg/issues/1322
+# See https://github.com/uclouvain/openjpeg/commit/aaddbc7
+diff -urNad openjpeg-2.3.1-orig/doc/CMakeLists.txt openjpeg-2.3.1/doc/CMakeLists.txt
+--- openjpeg-2.3.1-orig/doc/CMakeLists.txt	2019-04-02 15:45:15.000000000 +0300
++++ openjpeg-2.3.1/doc/CMakeLists.txt	2021-01-09 11:07:56.124355015 +0200
+@@ -44,7 +44,7 @@
+
+   # install HTML documentation (install png files too):
+   install(DIRECTORY ${CMAKE_BINARY_DIR}/doc/html
+-    DESTINATION share/doc
++    DESTINATION ${OPENJPEG_INSTALL_DOC_DIR}
+     PATTERN ".svn" EXCLUDE
+   )
+ else()