Add net-http and uri as dependencies

As described in
https://www.ruby-lang.org/en/news/2020/12/25/ruby-3-0-0-released/, Ruby
3.0.0 promoted net-http and net-imap from stdlib. Adding net-http as a
dependency avoids "already initialized constant errors" if net-imap or
some other gem is included. uri is needed as well for a similar reason.

uri needs to be locked down because bundler v2.1.4 isn't happy with
v0.10.1 (https://gitlab.com/gitlab-org/gitlab/-/jobs/1114901581):

```
Gem::LoadError: You have already activated uri 0.10.0, but your
Gemfile requires uri 0.10.1. Since uri is a default gem, you can either
remove your dependency on it or try updating to a newer version of
bundler that supports uri as a default gem.
```

Gemfile

@@ -440,6 +440,10 @@ gem 'octokit', '~> 4.15'
 
 # https://gitlab.com/gitlab-org/gitlab/issues/207207
 gem 'gitlab-mail_room', '~> 0.0.10', require: false
+# Ruby v3.0 promoted net-http and net-imap from stdlib. Adding net-http as a
+# dependency avoids "already initialized constant errors" if net-imap is installed.
+gem 'net-http', '~> 0.1'
+gem 'uri', '= 0.10.0' # Lock this for bundler v2.1.4
 
 gem 'email_reply_trimmer', '~> 0.1'
 gem 'html2text'

Gemfile.lock

@@ -765,6 +765,9 @@ GEM
       mustermann (>= 1.0.0)
     nap (1.1.0)
     nenv (0.3.0)
+    net-http (0.1.1)
+      net-protocol
+      uri
     net-http-persistent (4.0.1)
       connection_pool (~> 2.2)
     net-imap (0.2.1)
@@ -1286,6 +1289,7 @@ GEM
       equalizer (~> 0.0.9)
       parser (>= 2.6.5)
       procto (~> 0.0.2)
+    uri (0.10.0)
     uri_template (0.7.0)
     valid_email (0.1.3)
       activemodel
@@ -1497,6 +1501,7 @@ DEPENDENCIES
   mini_magick (~> 4.10.1)
   minitest (~> 5.11.0)
   multi_json (~> 1.14.1)
+  net-http (~> 0.1)
   net-ldap (~> 0.16.3)
   net-ntp
   net-ssh (~> 6.0)
@@ -1605,6 +1610,7 @@ DEPENDENCIES
   unicorn (~> 5.5)
   unicorn-worker-killer (~> 0.4.4)
   unleash (~> 0.1.5)
+  uri (= 0.10.0)
   valid_email (~> 0.1)
   validates_hostname (~> 1.0.11)
   version_sorter (~> 2.2.4)