Implement getAppManifests, getAppMarketplaceUrl and installApp operat…

[yiyangli-okta]

…ions

• Add some strings to XmlElementNames, add some enum to ExchangeVersion
• Implementation the corresponding *Request and *Response
• Add ComplexProperty ClientApp and ClientAppMetadata

[azurecla]

Hi @yiyangli-okta, I'm your friendly neighborhood Azure Pull Request Bot (You can call me AZPRBOT). Thanks for your contribution!

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[yiyangli-okta]

Signed.

[codecov-io]

Current coverage is 10.35% (diff: 2.53%)

No coverage report found for master at 7f8793a.

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[azurecla]

@yiyangli-okta, Thanks for signing the contribution license agreement so quickly! Actual humans will now validate the agreement and then evaluate the PR.

Thanks, AZPRBOT;