Redirect old SPO course links to moved or related pages

[rphair]

Fixes #1258. There weren't any "broken" links (as identified in the issue) on the Dev Portal itself; which can still be tested with something like

find blog changelog docs examples scripts static -L -type f -print0 | xargs -0 grep stake-pool-course

... only an obsolete anchor on the site Overview page and the obsolete section still listed in the file tree on portal-contribute.md. Therefore the affected links are 1) only in the SPO section (unless contradicted in #1258) and 2) are fixed by installing sensible redirects here (since there will never again be actual content at those pages).

There aren't many subjective decisions here, but one of them was redirecting /docs/stake-pool-course/handbook/setup-firewall to the beginning of /docs/operate-a-stake-pool/hardening-server/ rather than the Firewall section within that page (due to the old & new contexts being slightly different). Any further suggestions please feel free to mark them up in your review.

Tested in local build ✅ along with selected redirects copy/pasted as they would be when appearing in external sites.

cc @klntsky @katomm

[rphair]

@sanskys since you worked a lot on this material maybe you would also review this & see if you can come up with any improvements.

[sanskys]

@sanskys since you worked a lot on this material maybe you would also review this & see if you can come up with any improvements.

sure.. will have a look into it in coming weeks.

[rphair]

sure.. will have a look into it in coming weeks.

thanks @sanskys ... then it's probably best for us to merge this now & if you want to make adjustments later, you can do another PR or just send me the adjustments I I'll submit them.