docs: Republish the sizing calculator but don't list it in the table of contents and don't index it

[jdbaldry]

What this PR does / why we need it:
The link to the Loki public sizing calculator displays “We can’t find this page….” ?
Is this an error, or are we intending to stop using this public calculator?

The calculator was removed in #12598 because it was deemed to be too inaccurate but SEs would like to continue to use it with that understanding.

Which issue(s) this PR fixes:
https://raintank-corp.slack.com/archives/C01LEA0NMFT/p1714505902504099

[grafanabot]

Hello @jdbaldry!
Backport pull requests need to be either:

• Pull requests which address bugs,
• Urgent fixes which need product approval, in order to get merged,
• Docs changes.

Please, if the current pull request addresses a bug fix, label it with the type/bug label.
If it already has the product approval, please add the product-approved label. For docs changes, please add the type/docs label.
If the pull request modifies CI behaviour, please add the type/ci label.
If none of the above applies, please consider removing the backport label and target the next major/minor release.
Thanks!

[grafanabot]

Hello @jdbaldry!
Backport pull requests need to be either:

• Pull requests which address bugs,
• Urgent fixes which need product approval, in order to get merged,
• Docs changes.

Please, if the current pull request addresses a bug fix, label it with the type/bug label.
If it already has the product approval, please add the product-approved label. For docs changes, please add the type/docs label.
If the pull request modifies CI behaviour, please add the type/ci label.
If none of the above applies, please consider removing the backport label and target the next major/minor release.
Thanks!