[feature] Hashtag federation (in/out), hashtag client API endpoints (#2032)

* update go-fed

* do the things

* remove unused columns from tags

* update to latest lingo from main

* further tag shenanigans

* serve stub page at tag endpoint

* we did it lads

* tests, oh tests, ohhh tests, oh tests (doo doo doo doo)

* swagger docs

* document hashtag usage + federation

* instanceGet

* don't bother parsing tag href

* rename whereStartsWith -> whereStartsLike

* remove GetOrCreateTag

* dont cache status tag timelineability

internal/uris/uri.go

@@ -20,6 +20,7 @@ package uris
 import (
 	"fmt"
 	"net/url"
+	"strings"
 
 	"github.com/superseriousbusiness/gotosocial/internal/config"
 	"github.com/superseriousbusiness/gotosocial/internal/regexes"
@@ -43,6 +44,7 @@ const (
 	ConfirmEmailPath = "confirm_email" // ConfirmEmailPath is used to generate the URI for an email confirmation link
 	FileserverPath   = "fileserver"    // FileserverPath is a path component for serving attachments + media
 	EmojiPath        = "emoji"         // EmojiPath represents the activitypub emoji location
+	TagsPath         = "tags"          // TagsPath represents the activitypub tags location
 )
 
 // UserURIs contains a bunch of UserURIs and URLs for a user, host, account, etc.
@@ -178,6 +180,13 @@ func GenerateURIForEmoji(emojiID string) string {
 	return fmt.Sprintf("%s://%s/%s/%s", protocol, host, EmojiPath, emojiID)
 }
 
+// GenerateURIForTag generates an activitypub uri for a tag.
+func GenerateURIForTag(name string) string {
+	protocol := config.GetProtocol()
+	host := config.GetHost()
+	return fmt.Sprintf("%s://%s/%s/%s", protocol, host, TagsPath, strings.ToLower(name))
+}
+
 // IsUserPath returns true if the given URL path corresponds to eg /users/example_username
 func IsUserPath(id *url.URL) bool {
 	return regexes.UserPath.MatchString(id.Path)