Use forge from db (#1417)

This is the first step towards support for multiple forges (#138). It
inserts a forge using the currently existing env varaibles into db and
uses this forge from db later on in all places of the code.

closes #621

addresses #138 

# TODO
- [x] add forges table
- [x] add id of forge to repo
- [x] use forge of repo
- [x] add forge from env vars to db if not exists
- [x] migrate repo.ForgeID to the newly generated forge
- [x] support cache with forge from repo
- [x] maybe add forge loading cache? (use LRU cache for forges, I expect
users to have less than 10 forges normally)

---------

Co-authored-by: qwerty287 <80460567+qwerty287@users.noreply.github.com>

web/src/views/repo/RepoWrapper.vue

@@ -77,7 +77,7 @@ const router = useRouter();
 const i18n = useI18n();
 const config = useConfig();
 
-const { forge } = useConfig();
+const { forge } = useConfig(); // TODO: remove this and use the forge type from the corresponding repo
 const repo = repoStore.getRepo(repositoryId);
 const repoPermissions = ref<RepoPermissions>();
 const pipelines = pipelineStore.getRepoPipelines(repositoryId);