SQSERVICES-1519 IdP for SAML that was overridden by update cannot be added again

[battermann]

https://wearezeta.atlassian.net/browse/SQSERVICES-1519

Old behavior

When an IdP was updated, the entry in the table issuer_idp_v2 did not get overridden, but instead a new entry was made. Because the old entry still existed, adding the old IdP again failed.

Changes

In this PR, on IdP update, old issuers in issuer_idp_v2 will be deleted. Not sure if this is the correct fix, as those old issuers may serve some other purpose that I am not aware of?

Checklist

• The PR Title explains the impact of the change.
• The PR description provides context as to why the change should occur and what the code contributes to that effect. This could also be a link to a JIRA ticket or a Github issue, if there is one.
• changelog.d contains the following bits of information (details):
  • A file with the changelog entry in one or more suitable sub-sections. The sub-sections are marked by directories inside changelog.d.

[fisx]

if spar crashes at the right moment, this will cause the old idp to be deleted and the new not to be introduced, which is not fixable over the rest api (let alone the UI).

I don't see a good way around this, though. It would be really nice to have transactions and postgres and everything. but i would like to have the comment below reflect this. (could you maybe also fix my typo there while you're at it ("epected")?)

[battermann]

I moved the deletion to the end which leaves a less inconsistent state, in the case of a failure. And I added a comment.