Be able to manually start and stop proxy

[vdanti]

[ISSUE]

Currently the proxy is automatically started / configured on session creation, and automatically stopped on session deletion (or on unexpected exception). You don't have the control on it.

So it can be good to be able to start & stop the proxy manually :

• to have better control on your tests flow
• to restart the proxy on the fly / on demand if you deal with broken network connection during your tests

[SOLUTION]

• Rename the existing capability appium:intercept to appium:startProxyAutomatically
• If capability appium:startProxyAutomatically is set to true : start the proxy during session creation
• If capability appium:startProxyAutomatically is set to false : the session will be created but the proxy will not be started until you start it manually
• In both cases, stop the proxy when session is deleted (and when an unexpected exception occurs)
• Add 2 new commands startProxy + stopProxy
• Create 2 private functions setupProxy(...) + clearProxy(...) that are called both in automatic mode and manual mode
• Fix duplicate imports of ./logger (imported as log and logger - keep log one)
• Refactor plugin.ts (by creating a getSessionProxy(...) which is called from all the commands)
• Rework logs
• Update readme
• Update docs/commands