rgw:admin/Fix update op mask bug in modify user method

[hasantir]

When we use ModifyUser method for update user opMask, dont work because of url annotation dont set in User model
I set url=op-mask in User model that sends opMask field value in url and op mask value apply on user correctly

Checklist

• Added tests for features and functional changes
• Public functions and types are documented
• Standard formatting is applied to Go code
• Is this a new API? Added a new file that begins with //go:build ceph_preview
• Ran make api-update to record new APIs

New or infrequent contributors may want to review the go-ceph Developer's Guide including the section on how we track API Status and the API Stability Plan.

The go-ceph project uses mergify. View the mergify command guide for information on how to interact with mergify. Add a comment with @Mergifyio rebase to rebase your PR when github indicates that the PR is out of date with the base branch.

[phlogistonjohn]

Please include a few more details so we can validate this change, such as:

1. details about the bug you saw
2. an explanation of why/how this fixes said bug
3. a unit test validating the behavior

We also prefer contributions include a Signed-off-by tag in the git commit. Thanks!

[hasantir]

Please include a few more details so we can validate this change, such as:

1. details about the bug you saw

2. an explanation of why/how this fixes said bug

3. a unit test validating the behavior

We also prefer contributions include a Signed-off-by tag in the git commit. Thanks!

Hello
I added some detail about bug in pull request description

[phlogistonjohn]

That's great, thanks very much.
I hope you find time to add a unit test, thanks!