enhance(schedule): add next run field to schedule

[wsan3]

Description

Add a "next run" field to the schedule object so that we can display when a schedule is going to run NEXT.

Desired View

Related

go-vela/community#871

[codecov]

Codecov Report

Attention: Patch coverage is 87.50000% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 68.08%. Comparing base (178e678) to head (7acd04d).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1131      +/-   ##
==========================================
+ Coverage   68.06%   68.08%   +0.02%     
==========================================
  Files         410      410              
  Lines       13699    13715      +16     
==========================================
+ Hits         9324     9338      +14     
- Misses       3841     3842       +1     
- Partials      534      535       +1     

Files	Coverage Δ
api/types/schedule.go	100.00% <100.00%> (ø)
database/schedule/update.go	76.47% <ø> (ø)
mock/server/schedule.go	0.00% <ø> (ø)
database/types/schedule.go	96.92% <66.66%> (-3.08%)	⬇️