[feature] add rate limit middleware (#741)

* feat: add rate limit middleware

* chore: update vendor dir

* chore: update readme with new dependency

* chore: add rate limit infos to swagger.md file

* refactor: add ipv6 mask limiter option

Add IPv6 CIDR /64 mask

* refactor: increase rate limit to 1000

Address https://github.com/superseriousbusiness/gotosocial/pull/741#discussion_r945584800

Co-authored-by: tobi <31960611+tsmethurst@users.noreply.github.com>

vendor/github.com/ulule/limiter/v3/rate.go

@@ -0,0 +1,53 @@
+package limiter
+
+import (
+	"strconv"
+	"strings"
+	"time"
+
+	"github.com/pkg/errors"
+)
+
+// Rate is the rate.
+type Rate struct {
+	Formatted string
+	Period    time.Duration
+	Limit     int64
+}
+
+// NewRateFromFormatted returns the rate from the formatted version.
+func NewRateFromFormatted(formatted string) (Rate, error) {
+	rate := Rate{}
+
+	values := strings.Split(formatted, "-")
+	if len(values) != 2 {
+		return rate, errors.Errorf("incorrect format '%s'", formatted)
+	}
+
+	periods := map[string]time.Duration{
+		"S": time.Second,    // Second
+		"M": time.Minute,    // Minute
+		"H": time.Hour,      // Hour
+		"D": time.Hour * 24, // Day
+	}
+
+	limit, period := values[0], strings.ToUpper(values[1])
+
+	p, ok := periods[period]
+	if !ok {
+		return rate, errors.Errorf("incorrect period '%s'", period)
+	}
+
+	l, err := strconv.ParseInt(limit, 10, 64)
+	if err != nil {
+		return rate, errors.Errorf("incorrect limit '%s'", limit)
+	}
+
+	rate = Rate{
+		Formatted: formatted,
+		Period:    p,
+		Limit:     l,
+	}
+
+	return rate, nil
+}