Jira Connect: replace reloadPage with fetchSubscriptions action

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Once OAuth is the status quo for Jira Connect authentication (#355048 (closed)), we no longer need to refresh the page when users take action on subscriptions (add or remove them).

This issue is to remove any uses of the reloadPage util, and replace the with the fetchSubscriptions Vuex action. This will fetch the subscriptions asynchronously and update the UI without required a page reload.