Stabilize Domain Manager Role Standard (#586)

As discussed in Team IaaS on 2024-11-13.

Details:

* Stabilize Domain Manager Role Standard

Moves Domain Manager Standard from Draft to Stable

* Restructure standard to align with updated template
* Remove outdated limitation not applicable to 2024.1
* Add info admonition banner for upcoming native integration
* Add stabilization date
* Restructure and update Domain Manager standard

Split standard into standard document and implementation notes.
Move the downstream policy-based implementation into the implementation
notes and differentiate instructions based on the Keystone release used.
Add the upstream spec to related documents and update the standard
according to the latest changes.

* Be more explicit about upgrade to native integration
* Address review comments
* Update Standards/scs-0302-w1-domain-manager-implementation-notes.md
* Change stabilized_at to a closer date (not in the past)
* update date again, harmonize with others

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Signed-off-by: Markus Hentsch <[email protected]>
Signed-off-by: Markus Hentsch <[email protected]>
Signed-off-by: Matthias Büchse <[email protected]>
Co-authored-by: josephineSei <[email protected]>
Co-authored-by: Matthias Büchse <[email protected]>