fix(UI): fix usage of $.ajax by going VanillaJS

[blizzz]

chaining .success() and .fail() was not working anymore, and jQuery is to be deprecated anyway. A step thereto! Also clears metadata step after an unsuccessful save to not be misleading.

Fixes

TypeError: $.ajax(...).fail(...).success is not a function

Uncaught TypeError: $.ajax(...).fail(...).success is not a function
    testMetaData https://cloud.example.com/apps/user_saml/js/admin.js?v=4456f07a-2:139
    success https://cloud.example.com/apps/user_saml/js/admin.js?v=4456f07a-2:155
    onload https://cloud.example.com/apps/user_saml/js/admin.js?v=4456f07a-2:96
    updateProvider https://cloud.example.com/apps/user_saml/js/admin.js?v=4456f07a-2:94
    setSamlConfigValue https://cloud.example.com/apps/user_saml/js/admin.js?v=4456f07a-2:166
    ve https://cloud.example.com/dist/core-main.js?v=4456f07a-2:1
    i https://cloud.example.com/dist/core-main.js?v=4456f07a-2:1
    k https://cloud.example.com/dist/core-main.js?v=4456f07a-2:1
    promise callback*requirePasswordConfirmation https://cloud.example.com/dist/core-main.js?v=4456f07a-2:1
    setSamlConfigValue https://cloud.example.com/apps/user_saml/js/admin.js?v=4456f07a-2:147
    <anonymous> https://cloud.example.com/apps/user_saml/js/admin.js?v=4456f07a-2:322
    u https://cloud.example.com/dist/core-common.js?v=4456f07a-2:1
    d https://cloud.example.com/dist/core-common.js?v=4456f07a-2:1
    setTimeout handler*74692/</Deferred/then/o/< https://cloud.example.com/dist/core-common.js?v=4456f07a-2:1
    l https://cloud.example.com/dist/core-common.js?v=4456f07a-2:1
    add https://cloud.example.com/dist/core-common.js?v=4456f07a-2:1
    then https://cloud.example.com/dist/core-common.js?v=4456f07a-2:1
    Deferred https://cloud.example.com/dist/core-common.js?v=4456f07a-2:1
    then https://cloud.example.com/dist/core-common.js?v=4456f07a-2:1
    <anonymous> https://cloud.example.com/apps/user_saml/js/admin.js?v=4456f07a-2:320
    dispatch https://cloud.example.com/dist/core-common.js?v=4456f07a-2:1
    handle https://cloud.example.com/dist/core-common.js?v=4456f07a-2:1
admin.js:139:7