Adds User-Agent header to requests

[splch]

includes cirq and cirq_ionq versions for deprecation warnings

[viathor]

What is the rationale for sending all this information? I don't think the server needs to know client's OS to execute quantum circuits. Note that User-Agent header is not actually required (at least in HTTP 1.1), see section 14.43 of RFC 2616:

14.43 User-Agent

   The User-Agent request-header field contains information about the
   user agent originating the request. This is for statistical purposes,
   the tracing of protocol violations, and automated recognition of user
   agents for the sake of tailoring responses to avoid particular user
   agent limitations. User agents SHOULD include this field with
   requests. The field can contain multiple product tokens (section 3.8)
   and comments identifying the agent and any subproducts which form a
   significant part of the user agent. By convention, the product tokens
   are listed in order of their significance for identifying the
   application.

       User-Agent     = "User-Agent" ":" 1*( product | comment )

   Example:

       User-Agent: CERN-LineMode/2.15 libwww/2.17b3

Perhaps we can send cirq version only? WDYT? Ideally, we'd have an issue about it where we could discuss the problem and potential solutions.

[splch]

What is the rationale for sending all this information? I don't think the server needs to know client's OS to execute quantum circuits. Note that User-Agent header is not actually required (at least in HTTP 1.1), see section 14.43 of RFC 2616:

14.43 User-Agent

   The User-Agent request-header field contains information about the
   user agent originating the request. This is for statistical purposes,
   the tracing of protocol violations, and automated recognition of user
   agents for the sake of tailoring responses to avoid particular user
   agent limitations. User agents SHOULD include this field with
   requests. The field can contain multiple product tokens (section 3.8)
   and comments identifying the agent and any subproducts which form a
   significant part of the user agent. By convention, the product tokens
   are listed in order of their significance for identifying the
   application.

       User-Agent     = "User-Agent" ":" 1*( product | comment )

   Example:

       User-Agent: CERN-LineMode/2.15 libwww/2.17b3

Perhaps we can send cirq version only? WDYT? Ideally, we'd have an issue about it where we could discuss the problem and potential solutions.

The idea was to return a similar UA string, but we don't need OS for debugging user issues. We mostly need cirq and ionq versions, but the python version is useful for particularly unexpected bugs. How does Python, Cirq, and Cirq-Ionq versions sound to you?

[vtomole]

How does Python, Cirq, and Cirq-Ionq versions sound to you?

cirq and cirq-ionq versions are always the same so this will be redundant.