miniorange_saml_sp_issuer not set correctly when using "Upload Metadata URL"

Problem/Motivation

On the "Service Provider Setup" page, if you enter a URL in the "Upload Metadata URL" field and click "Fetch Metadata", the
miniorange_saml_sp_issuer config value is set to $base_url in the upload_metadata() function. This should be set to this instead as it is in the submitForm() function:

  $sp_issuer = $base_url . '/samlassertion';

Steps to reproduce

1. Go to the "Service Provider Setup" page.
2. Enter a URL in the "Upload Metadata URL" field.
3. Click "Fetch Metadata".

miniorange_saml_sp_issuer config value is set to "https://example.com" instead of "'https://example.com/samlassertion".

Proposed resolution

1. Patch code to set miniorange_saml_sp_issuer config value correctly.
2. Commit change.