[Visual Search] Additional documentation, add discriminator types, up…

[shakao]

…date example to remove outdated actions

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[azuresdkci]

Can one of the admins verify this patch?

[AutorestCI]

Automation for azure-sdk-for-python

The initial PR has been merged into your service PR:
Azure/azure-sdk-for-python#3160

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[yangyuan]

LGTM

[hovsepm]

@shakao please fix the sample:

Validating "examples" and "x-ms-examples" in  specification/cognitiveservices/data-plane/VisualSearch/preview/v1.0/VisualSearch.json:
 error: 
operationId: Images_VisualSearch
scenario: Successful visual search
source: request
responseCode: ALL
severity: 0
errorCode: ONE_OF_MISSING
errorDetails:
  code: ONE_OF_MISSING
  params: []
  message: Data does not match any schemas from 'oneOf'
  path: paths//images/visualsearch/post/parameters/12
  description: >-
    The form data is an image binary. The Content-Disposition header's name
    parameter must be set to "image". You must specify an image binary if you do
    not use knowledgeRequest form data to specify the image; you may not use
    both forms to specify an image. You may specify knowledgeRequest form data
    and image form data in the same request only if knowledgeRequest form data
    specifies the cropArea field only  (it must not include an insights token or
    URL).
  inner:
    - code: INVALID_TYPE
      params:
        - file
        - string
      message: Expected type file but found type string
      path: paths//images/visualsearch/post/parameters/12

[shakao]

@hovsepm From previous PRs, I think this is a known issue with specifying "file" as the input type in the sample. Not sure if there's been a fix since, but I'm happy to update if you could point me to documentation on how to specify file inputs in the sample!