fix(SUP-39574): Enable captions button is not working

[Tzipi-kaltura]

Description of the Changes

the issue:
when the textLanguage config is defined to "auto" and there is no previous language in the localSession when clicking on enable caption button nothing happen.

root cause:
trying to find track with "auto" language and not real language

the solution:
when "captionsDisplay" is disabled change the attribute state to defaultLanguage (the playbackConfig.textLanguage after set the language for "auto")

CheckLists

• changes have been done against master branch, and PR does not conflict
• new unit / functional tests have been added (whenever applicable)
• test are passing in local environment
• Travis tests are passing (or test results are not worse than on master branch :))
• Docs have been updated