Separate install and update hooks

[bluebrown]

Describe the feature

Hi, I find it a bit problematic to have the same hook run on update and install. For example, treesitter, will error if this runs on the first installation:

use { 'nvim-treesitter/nvim-treesitter', run = ':TSUpdate' }

I think its because treesitter is not fully setup at this point yet. Once it has been installed, the command works as expected on subsequent updates.

I guess there are more situations where it makes sense to run some function on update but not on install. Hence it would be nice to have indivdual lifecycle hooks.

use { 
  'foo/bar', 
  onInstall = ':Something',
  onUpdate = ':Else',
}

[ppwwyyxx]

Also encountered the error on "TSUpdate".

[bluebrown]

@ppwwyyxx , in case of treesitter you can fix it like this.

 run = function()
      local ts_update = require("nvim-treesitter.install").update({ with_sync = true })
      ts_update()
    end,

But I still think splitting it into more than 1 lifecycle hook would make alot of sense.