patch 9.1.1231: filetype: SPA JSON files are not recognized

Problem:  filetype: SPA (single page application) JSON files are not
          recognized (used by pipewire and wireplumber)
Solution: detect pipewire and wireplumber configuration files as spajson
          filetype, include filetype, indent and syntax scripts for this
          new filetype (David Mandelberg).

I looked at all the files found by this command to see if the syntax
highlighting looked reasonable:

```
find {~/.config,/etc,/usr/share}/{pipewire,wireplumber} -type f -name \*.conf
```

References:
*   pipewire config files: https://docs.pipewire.org/page_config.html
*   wireplumber config files:
    https://pipewire.pages.freedesktop.org/wireplumber/daemon/configuration/conf_file.html
    and
*   https://pipewire.pages.freedesktop.org/wireplumber/daemon/locations.html

closes: #16950

Signed-off-by: David Mandelberg <david@mandelberg.org>
Signed-off-by: Christian Brabandt <cb@256bit.org>

.github/MAINTAINERS

@@ -285,6 +285,7 @@ runtime/ftplugin/slint.vim		@ribru17
 runtime/ftplugin/snakemake.vim		@ribru17
 runtime/ftplugin/solidity.vim		@cothi
 runtime/ftplugin/solution.vim		@dkearns
+runtime/ftplugin/spajson.vim		@dseomn
 runtime/ftplugin/spec.vim		@ignatenkobrain
 runtime/ftplugin/squirrel.vim		@ribru17
 runtime/ftplugin/ssa.vim		@ObserverOfTime
@@ -396,6 +397,7 @@ runtime/indent/scheme.vim		@evhan
 runtime/indent/scss.vim			@tpope
 runtime/indent/sh.vim			@chrisbra
 runtime/indent/solidity.vim		@cothi
+runtime/indent/spajson.vim		@dseomn
 runtime/indent/systemverilog.vim	@Kocha
 runtime/indent/tcl.vim			@dkearns
 runtime/indent/tcsh.vim			@dkearns
@@ -609,6 +611,7 @@ runtime/syntax/sed.vim			@dkearns
 runtime/syntax/shared/debversions.vim	@jamessan
 runtime/syntax/shaderslang.vim          @mTvare6
 runtime/syntax/solidity.vim		@cothi
+runtime/syntax/spajson.vim		@dseomn
 runtime/syntax/spec.vim			@ignatenkobrain
 runtime/syntax/sqloracle.vim		@chrisbra
 runtime/syntax/squirrel.vim		@zenmatic