The Xray APIs should not use ArtifactoryClientBuilder

[eyalbe4]

Describe the bug
Following the merge of #211 we should refactor the code, so that the new Xray APIs introduced in this PR do not use the ArtifactoryClientBuilder. We should either create a generic builder for all JFrog services, or alternatively create client APIs for Xray.
See the following comment as part of the above PR:

Now that ArtifactoryClientBuilder also needs to be used for Xray, we should rename it to HttpClientBuilder.
We should also move the httpclient package, which is currently located under the artifactory directory, to be one level up, next to the artifactory dir.
rthttpclient should be renamed to httpclient, or if the the httpclient is already taken as an alias in the file, maybe jfroghttpclient.

To Reproduce
N/A

Expected behavior
N/A

Screenshots
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Versions

• JFrog Go client version: N/A
• JFrog Go client operating system: N/A
• Artifactory version: N/A

[eyalbe4]

#255 resolves this issue.