UI: remove default setting for max_versions in kv metadata

[hellobontempo]

The default value of a secret's metadata was incorrectly setting max_versions to 10 which caused unintended side effects. This PR fixes #8656. Instead of setting the metadata's max_versions from the engine's config, leaving unset has the same result without manipulating any values under the hood.

The greater number takes precedence if both the engine and secret metadata have max_versions configured. Otherwise, 0 means unset and if neither have a max_versions value, Vault will keep the 10 latest versions.

global (engine)	secret metadata	*versions kept - why?!
0	0	But are unset so Vault keeps 10 versions
0	2*	The engine has no global max_versions so the metadata value is used
8*	0	Metadata max_versions is unset so the engine's value is used
3	5*	Metadata has a higher max_versions number
9*	2	Yep, you guessed it! The engine config is higher

Both metadata READ responses below have the same kv engine config:

# curl kv/config
=> "data": {
    "cas_required": false,
    "delete_version_after": "0s",
    "max_versions": 3
  }

# curl  kv/metadata/max-2
 => "data": {
    "cas_required": false,
    "created_time": "2023-08-17T03:29:14.58914Z",
    "current_version": 4,
    "custom_metadata": null,
    "delete_version_after": "0s",
    "max_versions": 2, # max_versions is 2 but below 3 are kept because that's the engine config
    "oldest_version": 2,
    "updated_time": "2023-08-17T03:31:09.852191Z",
    "versions": {
      "2": {
        "created_time": "2023-08-17T03:29:23.621884Z",
        "deletion_time": "",
        "destroyed": false
      },
      "3": {
        "created_time": "2023-08-17T03:30:58.966954Z",
        "deletion_time": "",
        "destroyed": false
      },
      "4": {
        "created_time": "2023-08-17T03:31:09.852191Z",
        "deletion_time": "",
        "destroyed": false
      }
    }
  }

# curl kv/metadata/max-5
 => "data": {
    "cas_required": false,
    "created_time": "2023-08-17T03:35:15.076621Z",
    "current_version": 6,
    "custom_metadata": null,
    "delete_version_after": "0s",
    "max_versions": 5, # even though the engine max_versions is 3, the metadata max is used because it's greater
    "oldest_version": 2,
    "updated_time": "2023-08-17T03:35:26.416381Z",
    "versions": {
      "2": {
        "created_time": "2023-08-17T03:35:17.780665Z",
        "deletion_time": "",
        "destroyed": false
      },
      "3": {
        "created_time": "2023-08-17T03:35:20.729444Z",
        "deletion_time": "",
        "destroyed": false
      },
      "4": {
        "created_time": "2023-08-17T03:35:22.889623Z",
        "deletion_time": "",
        "destroyed": false
      },
      "5": {
        "created_time": "2023-08-17T03:35:24.658798Z",
        "deletion_time": "",
        "destroyed": false
      },
      "6": {
        "created_time": "2023-08-17T03:35:26.416381Z",
        "deletion_time": "",
        "destroyed": false
      }
    }

Docs for engine max_versions

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[Monkeychip]

Thanks for tackling. Backport as far as to 1.12?

[hashishaw]

Thank you for the detailed description!