doxygen: restructure docs inputs

new top-level directory `/doxygen/` contains all common doxygen elements,
`Makefile.am` contents moved into `/gnuscripts/lalsuite_doxygen.am`.
31 jobs for top-level-doxygen in 117 minutes and 45 seconds (queued for 8 seconds)
Status Job ID Name Coverage
  .Pre
passed #543110
make-dist

00:06:05

 
  Lal
passed #543113
lal:conda:fftw

00:12:13

passed #543114
lal:conda:mkl

00:12:03

passed #543112
lal:deb

00:28:43

passed #543111
lal:rpm

00:13:58

 
  Lal Frame
passed #543117
lalframe:conda

00:08:49

passed #543116
lalframe:deb

00:04:34

passed #543115
lalframe:rpm

00:02:42

 
  Lal Meta Io
passed #543120
lalmetaio:conda

00:08:23

passed #543119
lalmetaio:deb

00:05:08

passed #543118
lalmetaio:rpm

00:03:08

 
  Lal Simulation
passed #543123
lalsimulation:conda

00:10:55

passed #543122
lalsimulation:deb

00:15:31

passed #543121
lalsimulation:rpm

00:05:55

 
  Lal Burst
passed #543126
lalburst:conda

00:10:40

passed #543125
lalburst:deb

00:15:50

passed #543124
lalburst:rpm

00:10:01

 
  Lal Inspiral
passed #543129
lalinspiral:conda

00:14:09

passed #543128
lalinspiral:deb

00:15:35

passed #543127
lalinspiral:rpm

00:07:38

 
  Lal Pulsar
passed #543132
lalpulsar:conda

00:12:44

passed #543131
lalpulsar:deb

00:17:24

passed #543130
lalpulsar:rpm

00:08:43

 
  Lal Inference
passed #543135
lalinference:conda

00:17:23

passed #543134
lalinference:deb

00:08:54

passed #543133
lalinference:rpm

00:08:02

 
  Lal Apps
passed #543138
lalapps:conda

00:18:06

passed #543137
lalapps:deb

00:13:18

passed #543136
lalapps:rpm

00:07:40

 
  Documentation
passed #543139
documentation

00:07:19

 
  Integration Tests
passed #543140
top-level

00:44:39