feat: add support of openmetrics (#144)

* feat: add openmetrics support & endpoint

* add support of named resources

* update docstrings

* generate docs

* add another test for http api

package/archlinux/PKGBUILD

@@ -75,6 +75,7 @@ package_ahriman-web() {
     depends=("$pkgbase-core=$pkgver" 'python-aiohttp-cors' 'python-aiohttp-jinja2')
     optdepends=('python-aioauth-client: OAuth2 authorization support'
                 'python-aiohttp-apispec>=3.0.0: autogenerated API documentation'
+                'python-aiohttp-openmetrics: HTTP metrics support'
                 'python-aiohttp-security: authorization support'
                 'python-aiohttp-session: authorization support'
                 'python-cryptography: authorization support')