Load improvements related to MR widget

What does this MR do?

• Stop using the MergeRequestEntity to load sidebar features (use MergeRequestBasicEntity instead)
• Drop merge_check endpoint (use only show action for load/polling)
• Remove unnecessary initial request to load the widget (we were previously making a request to merge_check)
• Set proper header to be used on FE polling
• Add query count tests

Related to gitlab-ee!1933

Related to https://gitlab.com/gitlab-org/gitlab-ce/issues/32536

EE MR: https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/1935

cc @yorickpeterse

changed the description

added 2 commits

• 7efa0aa0 - Remove unnecessary initial request
• a355bcac - Stop loading MergeRequestEntity data on sidebar request

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changed the description

mentioned in issue #31934 (closed)

added 1 commit

• 92cdf78d - Fix Karma expect

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changed the description

added 1 commit

• ca5f9955 - Remove route

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changed the description

mentioned in issue #32536 (closed)

added 1 commit

• 72fb9999 - Remove merge_check_path from MR entity

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added 1 commit

• 74d0ed6d - 1 commit from branch master

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added 1 commit

• 3e08713c - Remove route

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added 1 commit

• 74d0ed6d - 1 commit from branch master

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added 1 commit

• 3e08713c - Remove route

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added 1 commit

• 3e08713c - Remove route

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added 1 commit

• b3cf3d04 - Make sure fixture creation does not affect query count test

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@fatihacet Could you also merge this, since gitlab-ee!1935 got merged?

approved this merge request

EE is reviewed and merged. Merging this one too.

Thanks @oswaldo

merged

mentioned in commit 5460153c

added regression label

changed the description

mentioned in commit 677229bb

Picked into 9-2-stable, will go in 9-2-1.

mentioned in issue gitaly#264 (closed)

resolved all discussions