AUTH UI: after login, needs to redirect to "return URL"

### Title: Handle Return URL

## Description:

The Cooperatives web app redirects to the Auth UI if the necessary Keycloak tokens are not present. The Auth UI currently routes to the Manage Businesses dashboard after successful login.

Now there are additional web apps that require a logged in user (eg, PPR, Create Business). As above, they will redirect to the Auth UI if the necessary Keycloak tokens are not present. However, the Auth UI should redirect back to the subject app after successful login. To accomplish this, the web apps will provide a Return URL as part of the Auth URL. The Auth UI needs to redirect back to that Return URL after login.

The expected URL format is, for example:
`https://dev.bcregistry.ca/cooperatives/auth/[Return URL]`
where [Return URL] is URL-encoded and may contain URL params for the originating web page, eg:
`https://dev.bcregistry.ca/cooperatives/dashboard?filing_id=1234`.

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* As a user
* I want to be redirected back to my originating web page after login
* so that I can simply save a bookmark to the web app I care about.

**Acceptance Criteria**
* GIVEN ... (you or your condition)
* WHEN ... (what you do)
* THEN ... (what you see)

**Dependencies? (If so, link dependency in the ticket, make it visible in a team´s backlog)**

**Validation Rules? (If yes, list here)**

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**DoR for User Story:**
- [ ] Do we have a prioritized Sprint Backlog?
- [ ] Defects, user stories and other work the team has committed to are contained in the sprint backlog?
- [ ] Any hidden work?
- [ ] All team members availability (days) & capacity (in SP) is known for the Sprint?
- [ ] All users stories meet the DoR?

**Definition of Ready:**
1. [ ] Does User Story have full flow of business rules, happy and alternate paths, etc.?
2. [ ] Requirements & expected behavior included in the User Story?
3. [ ] Are the dependencies known/ understood?
4. [ ] Dev team accepts user experience artifacts
5. [ ] If there are validation rules, are they defined (UI, Data, Role-Action)?
6. [ ] Does this User Story needs stakeholder approval?
7. [ ] Is this user story small enough to be completed in a Sprint?
8. [ ] What do we possible have to do re Change Management? - a) GCPE, …?

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**Definition of Done:**
1) [ ] Check Requirements against completed tasks
2) [ ] Completed stories verified in Dev and Test
3) [ ] Confirm Test cases built and succeeding
4) [ ] No regression test failures
5) [ ] Test coverage acceptable by Product Owner???
6) [ ] Ticket merged to master or story branch
7) [ ] Developer to list Config changes/ Update documents and designs
8) [ ] Design / Solution accepted by Product Owner
9) [ ] UX Approved
10) [ ] Can be demoed in Sprint Review
11) [ ] Release ticket is created and this US is linked to it