Prepare endpoint to connect a new github integration over Nango

[themarolt]

In the database we still want just one platform = github so the distinction has to be in the settings and it has to be set when connecting the integration.

We need a list of connections that are to be used with token rotation (stored in the db - new table githubTokenRotations) which are then passed as metadata to the nango connection being made.

There is also a distinction here between gerrit and github where we will have just one integrations row and multiple nango connections - 1 per repository. This means that the nango connections have to be mapped to 1 integrations row so in the settings column besides the repos we would also need mapping between a repo and a nango connection id.

Because of this change there will also be slight change in nango-webhook-api and nango-worker because they are assuming 1 integrations row = 1 nango connection which won't be the case here.