Allow multiple IDPs for SSO on Self Hosted Fluxer Instances

Fluxer currently only supports having one OIDC IDP. This could potentially be a blocker for specific organizations & deployments. (for example in certain organizations such as Academia/Research Institutions, Large scale organizations with multiple subsidiaries, or Government institutions, having multiple different IDPs is very common and often necessary)

Allow having multiple OIDC IDPs on one Fluxer instance I think the baseline already exists to implement this, the user traits of a user with SSO includes fields for what IDP they came from. So Fluxer could keep track of what users come from what IDPs in a multi-IDP environment in theory? I haven't dug too deep into the SSO logic that currently exists, so i cant say for sure