fix: secure variable migration token (#3394)

## Description

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Fixes #123
Fixes #456
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Closes #3172 

fix: add secure validation to migrationToken parameter

Implement input validation for the migrationToken parameter in the Bicep
template to ensure only authorized tokens are accepted.

This prevents potential misuse of the parameter and enhances the
security of the deployment process.


## Pipeline Reference

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## Type of Change

<!-- Use the checkboxes [x] on the options that are relevant. -->

- [ ] Update to CI Environment or utilities (Non-module affecting
changes)
- [ ] Azure Verified Module updates:
- [ ] Bugfix containing backwards-compatible bug fixes, and I have NOT
bumped the MAJOR or MINOR version in `version.json`:
- [ ] Someone has opened a bug report issue, and I have included "Closes
#{bug_report_issue_number}" in the PR description.
- [ ] The bug was found by the module author, and no one has opened an
issue to report it yet.
- [ ] Feature update backwards compatible feature updates, and I have
bumped the MINOR version in `version.json`.
- [ ] Breaking changes and I have bumped the MAJOR version in
`version.json`.
  - [ ] Update to documentation

## Checklist

- [ ] I'm sure there are no other open Pull Requests for the same
update/change
- [ ] I have run `Set-AVMModule` locally to generate the supporting
module files.
- [ ] My corresponding pipelines / checks run clean and green without
any errors or warnings

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---------

Co-authored-by: Erika Gressi <[email protected]>

avm/res/cognitive-services/account/main.bicep

@@ -102,6 +102,7 @@ param customerManagedKey customerManagedKeyType
 @description('Optional. The flag to enable dynamic throttling.')
 param dynamicThrottlingEnabled bool = false
 
+@secure()
 @description('Optional. Resource migration token.')
 param migrationToken string?
 

avm/res/cognitive-services/account/main.json

@@ -5,8 +5,8 @@
   "metadata": {
     "_generator": {
       "name": "bicep",
-      "version": "0.29.47.4906",
-      "templateHash": "259342811715055071"
+      "version": "0.30.23.60470",
+      "templateHash": "325704537018634474"
     },
     "name": "Cognitive Services",
     "description": "This module deploys a Cognitive Service.",
@@ -795,7 +795,7 @@
       }
     },
     "migrationToken": {
-      "type": "string",
+      "type": "securestring",
       "nullable": true,
       "metadata": {
         "description": "Optional. Resource migration token."
@@ -1784,8 +1784,8 @@
           "metadata": {
             "_generator": {
               "name": "bicep",
-              "version": "0.29.47.4906",
-              "templateHash": "986606208324987345"
+              "version": "0.30.23.60470",
+              "templateHash": "12263717469683062316"
             }
           },
           "definitions": {