[docs] Add the FAQ page in v6

[k-rajat19]

• I have followed (at least) the PR section of the contributing guide.

Fixes #14855

FAQ page has already been added for v7 in #11686 #13258

[mui-bot]

Deploy preview: https://deploy-preview-14857--material-ui-x.netlify.app/

Updated pages:

• docs/data/data-grid/faq/faq.md

Generated by 🚫 dangerJS against af7f0af

[MBilalShafi]

Hey @k-rajat19,

Thanks for raising the PR. 👍
I'll investigate the issue with the build.

[k-rajat19]

thanks for the reply
if possible, you can also give me some hints on where I should start the investigation to fix the netlify issue, I'll try to create a PR or directly push the changes here
thanks again!

[MBilalShafi]

Hey @k-rajat19,

Update on the failing build, some weird (most probably caching related) issue on the netlify consistently causes the build to fail on this PR, I tried a few fixes but didn't succeed. I opened another one (#14923) after clearing the cache and it finally passed.

I'll close this one in favor of #14923, thank you for the contribution anyways 🙏