Add Chrome try & ci CELab builder configs to mb_config.pyl.

This allows us to run CELab tests on Chrome.
"Choose tryjobs" now has two flavors of celab bots (chromium & chrome).

Chrome tests are needed for certain scenarios,
e.g. CloudManagementEnrollmentTokenTest: https://crrev.com/c/1779440

Config based on our existing Chromium bots, but added
'official' to get official chrome-branded builds:
  https://crrev.com/c/1841581

Which now works with the new bot & config:
  https://crrev.com/c/1836153

Based on https://crrev.com/i/1930512.

Bug: 1004563
Change-Id: Ia00cef7be4b0a6164e15b250052d867376edc139
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1836602Reviewed-by: Aaron Gable <agable@chromium.org>
Commit-Queue: Mathieu Binette <mbinette@google.com>
Cr-Commit-Position: refs/heads/master@{#703887}

tools/mb/mb_config.pyl

@@ -22,6 +22,7 @@
       'linux-chromeos-google-rel': 'official_goma_chromeos_minimal_symbols',
       'linux-google-rel': 'official_goma',
       'mac-google-rel': 'official_goma',
+      'win-celab-rel': 'official_celab_release_bot',
       'win-google-rel': 'official_goma_x86',
     },
 
@@ -733,6 +734,7 @@
       'linux-chrome': 'official_goma',
       'linux-chromeos-chrome': 'official_goma_chromeos_minimal_symbols',
       'win_chrome_official': 'official_goma_x86',
+      'win-celab-try-rel': 'official_celab_release_bot',
     },
 
     'tryserver.chromium.chromiumos': {
@@ -1781,6 +1783,10 @@
       'msan', 'release_bot',
     ],
 
+    'official_celab_release_bot': [
+      'official', 'release_bot', 'minimal_symbols',
+    ],
+
     # The cros chrome-sdk takes care of adding needed official/branding args
     # when using the sdk with '--internal'. So use the base cros_chrome_sdk
     # config here, but make sure the '--internal' argument is passed to the