Arch Linux

Description: list optional depends for prometheus

Additional info:
* package versions - glances 3.2.4-2
* config and/or log files etc. - none
* link to upstream bug report, if any - none

Steps to reproduce:

* install glances
* attempt to start a prometheus export

```
glances --export prometheus
Traceback (most recent call last):
File "/usr/bin/glances", line 33, in <module>
sys.exit(load_entry_point('Glances==3.2.4', 'console_scripts', 'glances')())
File "/usr/lib/python3.10/site-packages/glances/__init__.py", line 150, in main
start(config=core.get_config(), args= core.get_args())
File "/usr/lib/python3.10/site-packages/glances/__init__.py", line 109, in start
mode = GlancesMode(config=config, args=args)
File "/usr/lib/python3.10/site-packages/glances/standalone.py", line 53, in __init__
self.stats = GlancesStats(config=config, args=args)
File "/usr/lib/python3.10/site-packages/glances/stats.py", line 49, in __init__
self.load_modules(self.args)
File "/usr/lib/python3.10/site-packages/glances/stats.py", line 100, in load_modules
self.load_exports(args=args)
File "/usr/lib/python3.10/site-packages/glances/stats.py", line 175, in load_exports
export_module = __import__(self._exports_all[export_name])
File "/usr/lib/python3.10/site-packages/glances/exports/glances_prometheus.py", line 29, in <module>
from prometheus_client import start_http_server, Gauge
ModuleNotFoundError: No module named 'prometheus_client'
```

The package needed is `python-prometheus_client`