Add ability to provide custom key name for media type and query string

[Weffe]

Currently, the key names used for both Media Type and Query String are hardcoded as v and api-version respectively. It would be ideal to pass the key name in as a config option to withVersioning().

e.g.

For Media Type:

withVersioning(axios, {
  apiVersion: '2',
  versioningStrategy: VersioningStrategy.MediaType
  versionKeyName: 'my-custom-api-version' 
})

For Query String:

withVersioning(axios, {
  apiVersion: '2',
  versioningStrategy: VersioningStrategy.QueryString
  versionKeyName: 'my-custom-api-version' 
})

Maybe keyName can be ignored when the VersioningStrategy is UrlPath.

Something like this: https://codesandbox.io/s/k3j6p446kr?fontsize=14&view=editor

[Weffe]

Done. Implemented in commit dc3892f