[New Resource]: Added Verified Permissions identity_source

[DanielRieske]

Description

This PR adds the last resource identity_source to make this service complete.

Relations

Closes #35801
Closes #32158

References

Output from Acceptance Testing

% make testacc TESTARGS='-run=TestAccVerifiedPermissionsIdentitySource_' PKG=verifiedpermissions
make: Verifying source code with gofmt...
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go1.22.4 test ./internal/service/verifiedpermissions/... -v -count 1 -parallel 20  -run=TestAccVerifiedPermissionsIdentitySource_ -timeout 360m
=== RUN   TestAccVerifiedPermissionsIdentitySource_basic
=== PAUSE TestAccVerifiedPermissionsIdentitySource_basic
=== RUN   TestAccVerifiedPermissionsIdentitySource_update
=== PAUSE TestAccVerifiedPermissionsIdentitySource_update
=== RUN   TestAccVerifiedPermissionsIdentitySource_disappears
=== PAUSE TestAccVerifiedPermissionsIdentitySource_disappears
=== CONT  TestAccVerifiedPermissionsIdentitySource_basic
=== CONT  TestAccVerifiedPermissionsIdentitySource_disappears
=== CONT  TestAccVerifiedPermissionsIdentitySource_update
--- PASS: TestAccVerifiedPermissionsIdentitySource_disappears (19.98s)
--- PASS: TestAccVerifiedPermissionsIdentitySource_basic (22.33s)
--- PASS: TestAccVerifiedPermissionsIdentitySource_update (54.45s)
PASS
ok      github.com/hashicorp/terraform-provider-aws/internal/service/verifiedpermissions        58.785s

[github-actions]

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[DanielRieske]

Want to wait for #38192 to be merged to remove the expanders for the union types and fully use AutoFlex.