chore: Add migration for shared secret integration provider

[Dschoordsch]

Description

Preparations for #10360
For mattermost notifications we need to store a shared key and the server url in the integration provider. To make it explicit I added a new field for the key. The serverBaseURL field is already very fitting, so reusing that one.
Unlike the previous webhook integration, the provider will be used on org or global scope and does not have the channel information. This needs to go into the integration auth.

Demo

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Testing scenarios

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