fix(config): print only the value of config get and add display preferences

tea config get printed "key<TAB>value", so $(tea config get editor) was
not usable; it now prints the value alone, and --show-source appends the
source (D18). config get reads the instance's user, and instance settings
come from the selected instance (--host, TEA_HOST, default_host or the
sole instance). Unknown keys list the valid ones, and keys that need
--host or --user say so. config path no longer loads the settings, so it
works when hosts.yml is broken. config list is a table on a terminal.
config set confirms the change on a terminal and warns when default_host
has no account.

config.yml stores the hyperlinks (auto, always, never) and markdown
(auto, raw) preferences that tables and views now read, instead of the
TEA_HYPERLINKS and TEA_MARKDOWN variables. The environment table moves
out of tea config --help into tea help environment.

alias set refuses to replace an alias without --clobber, drops a leading
"tea", and explains how to quote an expansion with spaces or flags.
alias delete takes several names or --all, alias list is a table, and
an empty list says so on a terminal.

Signed-off-by: bircni <bircni@icloud.com>

internal/app/app_test.go

@@ -415,16 +415,11 @@ func walkCommands(cmd *cobra.Command, visit func(*cobra.Command)) {
 // have yet to complete; see TestHelpTextsAreComplete.
 const (
 	shortsToFix = `
-	config get
-	config list
 	notification mark-read
 	notification mark-unread
 	pr review cancel-request
 `
 	examplesToWrite = `
-	alias delete
-	alias list
-	alias set
 	api
 	auth login
 	auth logout
@@ -439,10 +434,6 @@ const (
 	branch rename
 	branch unprotect
 	branch view
-	config get
-	config list
-	config path
-	config set
 	doctor
 	issue attachment delete
 	issue attachment download
@@ -557,7 +548,6 @@ const (
 	wiki view
 `
 	longsToWrite = `
-	alias
 	auth
 	branch
 	issue