Add write.events.SIPNET function

[dlebauer]

Add function that converts a generic events.json (see #3621 and #3551) into sipnet-specific events.in files.

Description

Includes:

• write.events.SIPNET
• documentation w/ example
• tests

Motivation and Context

Required to use PEcAn to configure SIPNET to simulate agronomic managements.

Review Time Estimate

• Immediately
• Within one week
• When possible

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My change requires a change to the documentation.
• My name is in the list of CITATION.cff
• I agree that PEcAn Project may distribute my contribution under any or all of
  • the same license as the existing code,
  • and/or the BSD 3-clause license.
• I have updated the CHANGELOG.md.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[infotroph]

  Error ('test-write.events.SIPNET.R:9:5'): write.events.SIPNET produces expected lines
  Error in `vapply(evs, function(e) e$date, character(1))`: values must be type 'character',
   but FUN(X[[1]]) result is type 'list'
  Backtrace:
   1. PEcAn.SIPNET::write.events.SIPNET(ev_json1, outdir)
        at test-write.events.SIPNET.R:9:5
   3. base::vapply(evs, function(e) e$date, character(1))

@dlebauer seems like the proximal issue is the entries in events_site1.json being list instead of scalar, but I don't understand the intention behind that format enough to recommend a fix.

[infotroph]

@dlebauer reminder that this PR is still waiting for your input -- ping me if you want help on the test failures, but I'll need context from you to suggest the right fix.

[dlebauer]

@infotroph if you want to take another look at the changes that I've made (f800475...dlebauer:write_events_sipnet) while trying to get the tests to pass, they include

• move example events.json test fixtures to data.land package
• create a validate_events_json function that validates an events.json against the schema
  • add jsonlite and jsonvalidator to data.land suggests [not sure if this should be Imports?]
  • add jsonvalidator to PEcAn.SIPNET suggests (not sure if this is necessary,
  • add tests
  • use this function in write.configs.SIPNET()
  • as implemented, if jsonvalidate is not installed, it skips the test and returns validate = TRUE. This was to avoid haveing jsonvalidate in imports for a single function. But perhaps that is where it belongs.