Add FOAM_UUID variable for templates

[jkrenzer]

Is your feature request related to a problem? Please describe.

• Currently vscode snippet variabled are not accessable in metadata
• Thus, it is not possible to name a file with a UUIDv4 identifier

Describe the solution you'd like

• For the time being, as Allow snippet expansion without editor microsoft/vscode#155868 was closed it is not easily possbile to use an UUIDv4 for the filename/identifier
• It would be helpful to be able to introduce a FOAM_* variable to cover these cases
• Additionally it might be worthwhile to consider adding FOAM_* versions of RANDOM and HEXRANDOM, too. This way there would be more possibilities for non-chronological, uniform and unique file-naming.

Describe alternatives you've considered

• Running additional software to convert note files
  • Introduces additional dependencies and workflow steps
  • Might break some functionality of foam

Screenshots or Videos

No response