FAQ/TODO/KNOWN_BUGS: convert to markdown

- convert to markdown
- auto-generate the TOCs on the website, remove them from the docs
- cleanups
- spellchecked
- updated links

Closes #19875

.github/scripts/badwords.ok

@@ -4,4 +4,4 @@
 #
 # whitelisted uses of bad words
 # file:[line]:rule
-docs/FAQ::\bwill\b
+docs/FAQ.md::\bwill\b

.github/scripts/pyspelling.words

@@ -53,6 +53,7 @@ axTLS
 backend
 backends
 backoff
+backtick
 backticks
 balancers
 Baratov
@@ -171,8 +172,10 @@ dbg
 Debian
 DEBUGBUILD
 decrypt
+decrypted
 decrypting
 deepcode
+defacto
 DELE
 DER
 dereference
@@ -201,6 +204,7 @@ DLLs
 DNS
 dns
 dnsop
+DNSSEC
 DoH
 DoT
 doxygen
@@ -214,6 +218,7 @@ dynbuf
 EAGAIN
 EBCDIC
 ECC
+ECCN
 ECDHE
 ECH
 ECHConfig
@@ -258,6 +263,7 @@ Fedora
 Feltzing
 ffi
 filesize
+filesystem
 FindCURL
 FLOSS
 fnmatch
@@ -299,6 +305,7 @@ Ghedini
 giga
 Gisle
 Glesys
+glibc
 globbed
 globbing
 gmail
@@ -380,6 +387,7 @@ imap
 IMAPS
 imaps
 impacket
+implementers
 init
 initializer
 inlined
@@ -433,6 +441,7 @@ ldap
 LDAPS
 ldaps
 LF
+LGPL
 LGTM
 libbacktrace
 libbrotlidec
@@ -568,6 +577,7 @@ Necko
 NetBSD
 netrc
 netstat
+NetWare
 Netware
 NFS
 nghttp
@@ -711,6 +721,7 @@ ROADMAP
 Roadmap
 Rockbox
 roffit
+RPC
 RPG
 RR
 RRs
@@ -798,6 +809,7 @@ sprintf
 src
 SRP
 SRWLOCK
+SSI
 SSL
 ssl
 SSLeay
@@ -962,8 +974,10 @@ wcurl
 WebDAV
 WebOS
 webpage
+webpages
 WebSocket
 WEBSOCKET
+Wget
 WHATWG
 whitespace
 Whitespaces
@@ -982,6 +996,7 @@ www
 Xbox
 XDG
 xdigit
+XHTML
 Xilinx
 xmllint
 XP