Update issue templates

- Add template for issue type: Bug

Author: haithngn

.github/ISSUE_TEMPLATE/bug-report-template.md

@@ -0,0 +1,48 @@
+---
+name: Bug report template
+about: Describe this issue template's purpose here.
+title: "[Bug] - "
+labels: bug
+assignees: ''
+
+---
+
+**Summary**
+
+**Platform(s)**
+```
+<Android>
+```
+
+**Happens on Mail Server**
+```
+<Gmail>
+<iCloud>
+```
+
+**Piece of code**
+```
+MCOIMAPSession *session = [[MCOIMAPSession alloc] init];
+[session setHostname:@"imap.gmail.com"];
+[session setPort:993];
+[session setUsername:@"[email protected]"];
+[session setPassword:@"123456"];
+[session setConnectionType:MCOConnectionTypeTLS];
+```
+
+**Actual outcome**
+MailCore did or did not ...
+
+**Connection Logs**
+```
+* ID ("name" "GImap" "vendor" "Google, Inc." "support-url" "https://support.google.com/mail" "version" "gmail_imap_200623.09_p0" "remote-host" "2001:ee0:4fc
+5:b6e0:d410:e4d3:77db:fc8e
+```
+
+**Expected outcome**
+MailCore should ...
+
+**Link to sample code on GitHub reproducing the issue (a full Xcode project):**
+```
+https://
+```