doc/radosgw: Improve and more consistent formatting

doc/radosgw: Improve and more consistent formatting

Use inline code formatting consistently for command
line switches, data, hostnames, etc.
Correctly indent text and child lists in list items.
Remove a mid-sentence double spaces.
Capitalize "RGW" and "API" in text.
Remove unordered lists that are just regular text
everywhere else.
Use correct prompt # instead of $ for privileged
commands.
Use line continuation for multi-line example commands
instead of render them incorrectly as separate
single-line commands.
Use Title Case in few section header text that
missed it.
multisite.rst: Don't repeat "(RGW)" after "RADOS
Gateway" beyond the first instance in the same
paragraph.
multisite.rst: Change one "multisite" to "multi-site"
because all other instances use this spelling (EXCEPT
the title of the document??).
multisite.rst: Fix indentation of continuation lines in
prompted example commands.
Use pre-formatted block, as seen elsewhere in docs,
instead of strange unordered list plus inline code for
syntax example.
Add space before backslash for multi-line command
continuation.

Signed-off-by: Ville Ojamo <14869000+bluikko@users.noreply.github.com>
(cherry picked from commit a74f2e5f008691668884ebe3ed50eda6a9e0966e)