`PUT /hosts/{id}/device_mapping` should only trigger a resend of profiles when the IdP value changes

[lucasmrod]

Fleet version: 4.81.2

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Related to https://github.com/fleetdm/confidential/issues/14785.

💥  Actual behavior

PUT /api/_version_/fleet/hosts/{id}/device_mapping unconditionally triggers a resend of profiles with IdP variables, even if the email being set is the same email already set.

🛠️ To fix

• API request should no-op if the email being set is set already.
• Remove this from the API docs: Document PUT /hosts/{id}/device_mapping side effect #41514

🧑‍💻  Steps to reproduce

1. Configure a configuration profile with IdP e-mail variables.
2. Manually run PUT /api/_version_/fleet/hosts/{id}/device_mapping

[noahtalerman]

@lucasmrod thanks for tracking this. I see you added this to the #g-mdm board. For a bug to go into the current sprint, I think it needs P1. I added it now.

Then up to @georgekarrv.

cc @melpike @JordanMontgomery