Added network proxy support

[vitalytarasov]

This PR adds network proxy support as described in https://rokulikeahurricane.io/proxying_network_requests App-level proxying - this is the most common type of proxy for development of Roku channels. Default behavior is unchanged, proxy can be added using UpdateConfig method.

[CLAassistant]

All committers have signed the CLA.

[vitalytarasov]

@asllop & @cjmccarthy - any traction on this PR?

[asllop]

Hi, @vitalytarasov, sorry for the delay.

Your PR looks fine, with only a few objections:

• The function UpdateConfig doesn't follow the naming conventions. All methods start with "nr" (except the initializers and stoppers, that start with "NewRelic"). In your case, it should be nrUpdateConfig.
• There is no documentation at all. If you look at the README file, you will see there is a section (https://github.com/newrelic/video-agent-roku#agent-api) where we document all public methods of the agent. You should document the format of the input, possible values, meaning, warnings, when and how the method can be used, etc. Take other methods' doc as a reference to create yours.
• There is no interface function in the source/NewRelicAgent.brs file. All our public methods have a wrapper in there, to avoid having to use callFunc directly. The wrapper must also include documentation. Take the other definitions in the file as an example.
• Also, you should update the agent version following the semver rules.

[vitalytarasov]

@asllop - I have updated the PR to address your concerns.