SeqN Add activate and load to immediate_commands

[goetzrrGit]

Allow activate and load to be used in the @immediate section of a seqN, enabling the generation of 'immediate_activate' and 'immediate_load' in the SeqJson defined by this ticket: NASA-AMMOS/seq-json-schema#25. This would result in the following syntax:

@immediate
load('seq_name')
activate('seq_name')

[dandelany]

There is a PR for this in the schema repo here: NASA-AMMOS/seq-json-schema#26

Todo list for release:

• merge schema PR
• publish latest schema version to npm/pip registries
• Update jpl_sequence to support new version - @cartermak
• Update aerie-ui to support new version
  • change seq-json-schema version in package.json
  • update SeqN grammar
• Update aerie backend to support new version
  • change seq-json-schema version in package.json of sequencing server
  • other changes needed in EDSL/sequencing server?
• Include in (Aerie) release notes

[cartermak]

Re: jpl-sequence, that shouldn't be a blocker to this feature.

[dandelany]

Per discussion with @goetzrrGit - this required a bit more schema change which resets the checklist above. Draft PR here:

NASA-AMMOS/seq-json-schema#29

[dandelany]

Aerie PRs are ready for review for this:
backend: NASA-AMMOS/aerie#1600
frontend: #1543