doc: Fix link and improve Crimson doc

doc: Fix link and improve Crimson doc

Fix Seastar external link that was not working.
Capitalize consistently as Crimson, SeaStore in text.
Fix typos including in a label and in a ref using it.
Wrap text at column 80.
Remove unused highlight directive.
Fix article and hyphenation.
Try to reduce amount of commas in text and improve language.
Use already existing label and ref instead of section title for link.
Use confval role for configuration keys in text.
Use an autoclass reference instead of hardcoding URL.
Trim spaces at end of lines and convert tabs to spaces.
Use a colon instead of a hyphen pretending to be an em dash.

Signed-off-by: Ville Ojamo <git2233+ceph@ojamo.eu>