refactor: migrate admin-console client service to ts

[seaerchin]

Problem

Closes #1521 - refactors admin-console.client.service.js into two separate frontend services and writes adds tests for them

Solution

Rewrote the admin-console service as two separate services in typescript.
Followed backend structure and structured it as exampleService and billingService

Tests

1.tests for billingService/exampleService to ensure that api requests are being carried out and to ensure that errors are being thrown if promises are rejected

Manual tests

• Click on examples after logging in - there should be multiple examples loaded
• Login and create a form. Navigate to share and then click copy on Share Template. Open the copied url in another tab - the form should open as a template.
• Login and navigate to billing.
  1. entering an invalid eserviceId should have 0 logins
  2. entering a valid eserviceId should have the logins for the specified time period.

[liangyuanruo]

the JSDoc for getExampleForms is incomplete because i'm unsure how to describe them. the corresponding backend controller examples.controller doesn't have the documentation defined on the parameter/type. will ask around and write it up

Thanks, noted. Appreciate it if you could derive and fill in the backend JSDocs, if they're missing too?

Meanwhile, you should actually switch over to using the TS implementation and delete the old JS files. Don't forget to test on staging if you have to.

[seaerchin]

@liangyuanruo yep, i'm going to check with either @karrui or @mantariksh and fill in both fe/be documentation

[karrui]

some queries

[karrui]

lgtm, please add manual test steps for next release

[karrui]

This PR may have conflicts with #1573, please coordinate :P
@orbitalsqwib FYI

[seaerchin]

This PR may have conflicts with #1573, please coordinate :P
@orbitalsqwib FYI

talked to @orbitalsqwib on this. we finalized that i'll merge my PR in first and he'll rebase/merge off this accordingly. @karrui fyi

[liangyuanruo]

Code LGTM, do address/resolve Antariksh's comments before merging.