Move prometheus to mandatory deps

optional-requirements.txt

@@ -12,6 +12,3 @@ asyncpg>=0.20,<0.22
 python-olm>=3,<4
 pycryptodome>=3,<4
 unpaddedbase64>=1,<2
-
-#/metrics
-prometheus_client>=0.6,<0.9

requirements.txt

@@ -6,3 +6,4 @@ commonmark>=0.8,<0.10
 python-magic>=0.4,<0.5
 mautrix>=0.7.2,<0.8
 fbchat-asyncio>=0.6.19,<0.7
+prometheus_client>=0.6,<0.9