Support for db_default=... for defaults generated by Salesforce

• Add: Support for db_default field option in Django 5.0. It allows a seamless
  support of the defaultedOnCreate counterpart in Salesforce.
• Add: Support for Salesforce API 60.0 Spring '24.
• Change: Values of FloatField are now really float, not Decimal as previously.
• Fix: Compatibility with the current django-debug-toolbar #322
• Fix: Introspection inspectdb of custom editable name fields #308
• Add: FloatField is used by inspectdb for some metadata with negative decimal places
  that are new in API 60.0.
• Change: A license code is required also in the first half of lifetime of a LTS version
  unless the AGPL licence is accepted.
  Django 4.2 LTS will be unlocked together with unlocking 5.0 in August 2024
  in Django-salesforce 5.1 release.
• Change: License code validity may not transfer to the next django-salesforce version
  if sponsorship ended.