Since placeholder text is dynamically generated, make it optional via env var

[asimons04]

Is your feature request related to a problem? Please describe.
The text fields in post and comment forms are pretty self explanatory. The placeholder text makes them too busy and adds unnecessary confusion especially since it is randomly selected.

Describe the solution you'd like
Ideally, just remove the randomly selected placeholder text as it's not really adding much value.

If removing them entirely is off the table, then add some kind of global setting (e.g. env var DISABLE_PLACEHOLDERS=true) that will cause the placeholders.get() function in utils.ts to return an empty string.

Describe alternatives you've considered
I do a custom build and neuter the placeholders object in src/lib/util.ts as such:

export const placeholders = {
  get: (type: 'url' | 'post' | 'comment') => {
    return ''
  },
}