How-to AAI general

Every day, we stumble over the same old problems of VO managers and users. With this MR, we could try to catch some of the most frequent problems by an as-short-as-can-be howto:

• A) for end users in normal login
• B) for users being invited to groups
• C) for VO managers

Once finished, this page should be linked to in basically every ticket, especially once a new VO is created. Also hifis.net and login.helmholtz.de should link there.

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• Review here

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Related:

• https://codebase.helmholtz.cloud/hifis/overall/ux/-/issues/7#note_6148216
• https://codebase.helmholtz.cloud/hifis/overall/ux/-/issues/7#note_6148262
• https://codebase.helmholtz.cloud/hifis/overall/ux/-/issues/7#note_6148264

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In this MR:

• Created the simple page
• Clean up: moved the mixture that ended up as old users-how-to page, and split that to
  • a) further information (might even be deleted), and
  • b) OIDC agent related stuff.