fix: async behavior when creating/updating a spec

[bodom0015]

Problem

When saving a new appspec, the UI throws the following error:

# 404 error resulting from existence check
>     GET https://kubernetes.docker.internal/api/v1/services/yay 404
sendRequest @ request.ts:131
await in sendRequest (async)

# I thought that this "uncaught" error would just return undefined.. apparently that is not the case
>     Uncaught (in promise) Error: Not found - spec key not found
    at catchErrors (request.ts:175:1)
    at request (request.ts:203:1)
    at async AppSpecService.getServiceById (AppSpecService.ts:96:1)
    at async saveSpec (AddEditSpec.tsx:329:1)
catchErrors @ request.ts:175
request @ request.ts:203
await in request (async)
onClick @ AddEditSpec.tsx:375 

# This only appears in development mode, but "process" is usually a server-side thing...
>      Uncaught ReferenceError: process is not defined

Apparently we need a .catch clause when async/await will hit an error

Approach

• Remove async/await here, switch back to using a classic Promise
• Add a proper error handler

How to Test

Prerequisites:

• workbench-helm-chart checked out locally
• cd src/webui/
• User added to workbench-developers group in Keycloak

Test Steps:

1. Checkout this branch and run locally: make compile
2. Login to Workbench WebUI via Keycloak user
3. Navigate to My Catalog
4. Click the "Create New Application" button
5. Enter spec details:
   • key: anything
   • image: something
   • ports: 8888
6. Click Save
   • You should be redirected back to the My Catalog view
   • You should see your new application now appears in the list