NocoBase v1.8.20: Adjust the workflow variable API to support presetting an additional variable list

[Workflow] Adjust the workflow variable API to support presetting an additional variable list (#7439) by @mytharcher
[Workflow: Approval]
- Support using approval-related variables in custom notifications by @mytharcher
- Support updating the approval status after the end node terminates the execution by @mytharcher

[client]
- Fix an issue where, in certain scenarios, editing a record in the mobile record picker popup causes an error (#7444) by @zhangzhonghe
- required validation not working for attachment fields in subtable (#7431) by @katherinehhh
- Fix the issue where the icon was displayed incorrectly when the URL in the attachment URL field contained query parameters (#7432) by @mytharcher
[database]
- Fixed a MySQL syntax error that occurred when loading more in-app messages. (#7438) by @aaaaaajie
- Fixed precision issue for exported Number fields (#7421) by @aaaaaajie
[undefined] Fixed issue with filtering by date field only in MySQL external source (#7422) by @aaaaaajie
[Action: Import records] Fixed an issue where import failed when the table primary key was a single-line text (#7416) by @aaaaaajie
[Workflow]
- Complete the options for automatically deleting workflow execution status (#7436) by @mytharcher
- Fix issues related to the mobile menu in the workflow tasks (#7419) by @mytharcher
[Action: Import records Pro] Fixed unexpected update result when using string primary key in xlsx import. by @aaaaaajie