MM-13664 Cache external link metadata when populating post metadata (#10128)

* MM-13664 Added LinkMetadata types

* MM-13664 Use LinkMetadata when populating post metadata

* Fix unused import

* Fix index name on SQLite

* Finish adding unit tests

* Address feedback

* Increase max length of URL column to 2048 characters

store/storetest/mocks/ObjectCache.go

@@ -0,0 +1,97 @@
+// Code generated by mockery v1.0.0. DO NOT EDIT.
+
+// Regenerate this file using `make store-mocks`.
+
+package mocks
+
+import mock "github.com/stretchr/testify/mock"
+
+// ObjectCache is an autogenerated mock type for the ObjectCache type
+type ObjectCache struct {
+	mock.Mock
+}
+
+// AddWithDefaultExpires provides a mock function with given fields: key, value
+func (_m *ObjectCache) AddWithDefaultExpires(key interface{}, value interface{}) {
+	_m.Called(key, value)
+}
+
+// AddWithExpiresInSecs provides a mock function with given fields: key, value, expireAtSecs
+func (_m *ObjectCache) AddWithExpiresInSecs(key interface{}, value interface{}, expireAtSecs int64) {
+	_m.Called(key, value, expireAtSecs)
+}
+
+// Get provides a mock function with given fields: key
+func (_m *ObjectCache) Get(key interface{}) (interface{}, bool) {
+	ret := _m.Called(key)
+
+	var r0 interface{}
+	if rf, ok := ret.Get(0).(func(interface{}) interface{}); ok {
+		r0 = rf(key)
+	} else {
+		if ret.Get(0) != nil {
+			r0 = ret.Get(0).(interface{})
+		}
+	}
+
+	var r1 bool
+	if rf, ok := ret.Get(1).(func(interface{}) bool); ok {
+		r1 = rf(key)
+	} else {
+		r1 = ret.Get(1).(bool)
+	}
+
+	return r0, r1
+}
+
+// GetInvalidateClusterEvent provides a mock function with given fields:
+func (_m *ObjectCache) GetInvalidateClusterEvent() string {
+	ret := _m.Called()
+
+	var r0 string
+	if rf, ok := ret.Get(0).(func() string); ok {
+		r0 = rf()
+	} else {
+		r0 = ret.Get(0).(string)
+	}
+
+	return r0
+}
+
+// Len provides a mock function with given fields:
+func (_m *ObjectCache) Len() int {
+	ret := _m.Called()
+
+	var r0 int
+	if rf, ok := ret.Get(0).(func() int); ok {
+		r0 = rf()
+	} else {
+		r0 = ret.Get(0).(int)
+	}
+
+	return r0
+}
+
+// Name provides a mock function with given fields:
+func (_m *ObjectCache) Name() string {
+	ret := _m.Called()
+
+	var r0 string
+	if rf, ok := ret.Get(0).(func() string); ok {
+		r0 = rf()
+	} else {
+		r0 = ret.Get(0).(string)
+	}
+
+	return r0
+}
+
+// Purge provides a mock function with given fields:
+func (_m *ObjectCache) Purge() {
+	_m.Called()
+}
+
+// Remove provides a mock function with given fields: key
+func (_m *ObjectCache) Remove(key interface{}) {
+	_m.Called(key)
+}