change the attributes in generated cases

[ArcturusZhang]

Fixes #5151

Description

change these ahead of time to reduce the amount of changes in the regen PR of this PR

Changes including:

• Previously we write:

[NUnit.Framework.Test]
[NUnit.Framework.Ignore("...")]

because of the refactor, the above way is no longer valid, now the new way is:

using NUnit.Framework;

[Test]
[Ignore("...")]

sample collecting scripts are also modified to align with the new way to avoid those NUnit namespace to appear in sample codes.

• the sentence in the Ignore attribute has been changed to align with whatever we have in DPG samples. This is not part of the sample, we added there so that the test will not be run on CI.
• A new example is added to verify the cases with option bags in mgmt plane.
• Some strings in the sample is always written in formattable string style, now they are changed to be literal strings.
• The comment before each sample method has been removed.

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