[docs] Fix docs feedback widget not working

[cherniavskii]

I've noticed that feedback widget on MUI X docs website doesn't work:

The reason is missing FEEDBACK_URL was missing in MUI X env.

Preview: https://deploy-preview-4905--material-ui-x.netlify.app/x/advanced-components/

[mui-bot]

These are the results for the performance tests:

Test case	Unit	Min	Max	Median	Mean	σ
Filter 100k rows	ms	276.6	517.1	408.8	401.06	97.257
Sort 100k rows	ms	561.9	907.5	804.6	782.5	127.08
Select 100k rows	ms	91.1	200.2	180.1	157.1	37.904
Deselect 100k rows	ms	112.4	204.8	154.4	160.26	33.218

Generated by 🚫 dangerJS against ac8f9ba

[m4theushw]

It could be an environment variable set by Netlify.

@oliviertassinari @mbrookes Is there a reason that forces to use docs/.env instead of an envvar? I didn't find any comment considering this option in mui/material-ui#22885

[mbrookes]

I don't recall any specific reason, so probably just an implementation issue. I do remember that I found other issues (unrelated to this), but the record of those is lost in a Slack comment (I should really have opened a GitHub issue), and I haven't looked at it since. It certainly isn't perfect, so feel free to improve it in whatever way you see fit.

[cherniavskii]

I'll move it to Netlify environment then

[oliviertassinari]

Form my perspective, MUI X shouldn't have to do anything to benefit from this feature, it should be fully isolated in the main repository, so no env variables. I'm adding this note to: https://www.notion.so/mui-org/Docs-page-feedback-rating-58166afbb53649c9ab873e646a637c8a#1a2cf3e6196d4b218b67169f811e280a