feature: allow grouping daily notes by date.

[alpham]

I was trying to find a way to group the daily notes by year and month.
After looking at the codebase I found that it's possible to do so by templating the opts.daily_notes.folder and allow adding template variables for datetime in lua.

example:
lazy.nvim configs

return {
  "epwalsh/obsidian.nvim",
...
  opts = {
    ...
    daily_notes = {
      folder = "notes/dailies/%Y/%B"
      ...
    },
    ...
  },
...
}

output:

notes
└── dailies
    └── 2024
        ├── December
        │   ├── 2024-12-01.md
        │   ├── 2024-12-02.md
        │   ├── 2024-12-03.md