User cannot edit the index name after she adds it as "write to index" in index connector

[bhavyarm]

Kibana version: 7.7.0 BC7

Elasticsearch version: 7.7.0 BC7

Server OS version: from cloud

Browser version: chrome latest

Browser OS version: OS X

Original install method (e.g. download page, yum, from source, etc.): from staging

Describe the bug: User cannot edit the index name after she adds it as "write to index" in index connector. Both clicking on x or clicking delete doesn't work.

The only workaround seems to be you need to start typing in the name.

Steps to reproduce:

1. Go to alerting and actions under management and click on connectors and then create connectors
2. Choose index connector - add in name for the connector and in write to index - type in an existing index name (I had sample data installed so I picked e-commerce)
3. Try to change the name of the index to something else by either clicking on x or delete
4. Kibana doesn't do anything
5. You need to start typing another index name to change the index to which this connector is writing to.

Screenshots (if relevant):

Errors in browser console (if relevant):

Uncaught (in promise) TypeError: Cannot read property 'value' of undefined
    at _callee2$ (:9243/bundles/plugin/triggers_actions_ui/triggers_actions_ui.plugin.js:1)
    at l (:9243/bundles/kbn-ui-shared-deps/kbn-ui-shared-deps.js:288)
    at Generator._invoke (:9243/bundles/kbn-ui-shared-deps/kbn-ui-shared-deps.js:288)
    at Generator.forEach.e.<computed> [as next] (:9243/bundles/kbn-ui-shared-deps/kbn-ui-shared-deps.js:288)
    at asyncGeneratorStep (:9243/bundles/plugin/triggers_actions_ui/triggers_actions_ui.plugin.js:1)
    at _next (:9243/bundles/plugin/triggers_actions_ui/triggers_actions_ui.plugin.js:1)
    at :9243/bundles/plugin/triggers_actions_ui/triggers_actions_ui.plugin.js:1
    at new Promise (<anonymous>)
    at :9243/bundles/plugin/triggers_actions_ui/triggers_actions_ui.plugin.js:1
    at :9243/bundles/plugin/triggers_actions_ui/triggers_actions_ui.plugin.js:1

[elasticmachine]

Pinging @elastic/kibana-alerting-services (Team:Alerting Services)