Add the Cylc language.

[oliver-sanders]

Description

Add the Cylc language.

Checklist:

• I am adding a new language.
  • The extension of the new language is used in hundreds of repositories on GitHub.com.
    • Search results for each extension:
      • https://github.com/search?q=%28path%3A**%2Fsuite.rc+OR+path%3A**%2Fflow.cylc%29+-is%3Afork+-org%3Acylc&type=code&ref=advsearch
      • (note all Cylc projects must have a "root" flow.cylc or suite.rc file which is what I've searched for above, projects often contain additional "*.cylc" files)
  • I have included a real-world usage sample for all extensions added in this PR:
    • Sample source(s):
      • https://github.com/MetOffice/CSET/blob/main/cset-workflow/flow.cylc
      • https://github.com/MetOffice/CSET/tree/main/cset-workflow/includes
    • Sample license(s):
      • Apache 2.0
  • I have included a syntax highlighting grammar: Cylc.tmbundle (BSD)
  • I have added a color
    • Hex value: #00b3fd
    • Rationale: Primary brand colour used in user interfaces and the logo.
  • I have updated the heuristics to distinguish my language from others using the same extension.
    • No other languages share the ".cylc" extension.