Consistent usage of running pnpm and yarn scripts across documentation

[trueberryless]

Domain knowledge

pnpm and yarn offer two ways to run scripts from your package.json:

pnpm run <script>
pnpm <script>

yarn run <script>
yarn <script>

I will refer to the run version as "explicit variant". And I'll call the version without run "short variant" within this discussion.

Documentation for this is available for pnpm and yarn.

Proposal

I am proposing to consistently use either the explicit or short variant throughout all of Astro documentation to avoid confusion.
After discussion this initially with @ArmandPhilippot in this PR, I am strongly leaning toward using the explicit variant everywhere because of two reasons:

• It avoids confusion for newcomers (especially in the tutorial pages).
• It is already used more often than the short variant (33 explicit occurrences, 26 short occurrences¹).

The reason I think the Astro docs would benefit from such a refactor is to avoid confusion because of the inconsistency.
The refactor also wouldn't even be as big as I initially expected.

Please let me know your opinions and takes on this in the comments.

Footnotes

1. I checked out f8c0d55 and used this RegEx: (pnpm|yarn)\s+(?!(?:add|exec|create|astro))(\S+) to go through all 124 occurrences and counted manually.

   These are the detailed results:

   	Explicit	Short	Sum
   pnpm	19	11	30
   yarn	14	15	29
   Sum	33	26	59

   Please do not ask me why pnpm occurs one more time than yarn in total 😅

   One interesting fact I noticed while counting is: The different variants often occur in the same files and not - as I would have expected - separated in different files. In other words: The inconsistencies happen within files, and can not be grouped by files. ↩