doxygen from home:ecsos project

For openSUSE Slowroll run the following as root:

zypper addrepo https://download.opensuse.org/repositories/home:ecsos/openSUSE_Slowroll/home:ecsos.repo
zypper refresh
zypper install doxygen

For 15.5 run the following as root:

zypper addrepo https://download.opensuse.org/repositories/home:ecsos/15.5/home:ecsos.repo
zypper refresh
zypper install doxygen

For 16.0 run the following as root:

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