Fixes the following issues:

1. Fixed incorrect certificate download when changing a signing certificate - previously, clicking "Download Signing Certificate" after updating a certificate would still download the old certificate until the page was refreshed.
2. Fixed missing UI updates when adding a signing certificate - previously, when a signing certificate was added to a provider, the download button wouldn't appear until the page was refreshed.
3. Fixed persistent download button when removing a certificate - previously, when a signing certificate was removed from a provider, the download button would still be visible until the page was refreshed.

Closes #14310

Test cases:

Issue 1:

1. Create 2 certs under System > Certificates: cert1 and cert2
2. Edit the provider and set signing certificate to cert1 and download it
3. Now, edit and set it to cert2 and download it. cert2 should get downloaded this time

Issue 2:

1. Remove signing certificate and refresh. Now there's no cert and no button.
2. Add cert1 and click save and check if the download cert button appears.

Issue 3:

1. Edit the provider and remove cert1.
2. Check if the download cert button is gone.

Details

REPLACE ME

Checklist

• Local tests pass (ak test authentik/)
• The code has been formatted (make lint-fix)

If an API change has been made

• The API schema has been updated (make gen-build)

If changes to the frontend have been made

• The code has been formatted (make web)

If applicable

• The documentation has been updated
• The documentation has been formatted (make website)