Fix kind attribute update query in beta.17 to beta.18 migration guide

[samohovets]

Description of what you did:

During the migration, I ran into the problem while updating the kind attribute: in my repeatable components kind attribute was updated only in first element. I fixed it by using all positional operator $[] in update query.

Operator differences: https://docs.mongodb.com/manual/reference/operator/update-array/#array-update-operators

[codecov]

Codecov Report

Merging #7583 into documentation will increase coverage by 7.07%.
The diff coverage is n/a.

@@                Coverage Diff                @@
##           documentation    #7583      +/-   ##
=================================================
+ Coverage          19.14%   26.21%   +7.07%     
=================================================
  Files                855     1131     +276     
  Lines              11933    15440    +3507     
  Branches            1898     2438     +540     
=================================================
+ Hits                2284     4048    +1764     
- Misses              8100     9576    +1476     
- Partials            1549     1816     +267     

Flag	Coverage Δ
#front	18.25% <ø> (+3.76%)	⬆️
#unit	53.14% <ø> (+13.21%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
packages/strapi-plugin-email/admin/src/pluginId.js	0.00% <0.00%> (-100.00%)	⬇️
...n/src/containers/NotificationProvider/constants.js	0.00% <0.00%> (-100.00%)	⬇️
...i-admin/admin/src/containers/SettingsPage/index.js	0.00% <0.00%> (-66.67%)	⬇️
...trapi-admin/admin/src/containers/LeftMenu/index.js	5.00% <0.00%> (-61.67%)	⬇️
...n/admin/src/containers/LanguageProvider/reducer.js	0.00% <0.00%> (-61.54%)	⬇️
...in/admin/src/containers/Webhooks/ListView/index.js	0.00% <0.00%> (-42.11%)	⬇️
...in/admin/src/containers/Webhooks/EditView/index.js	0.00% <0.00%> (-38.40%)	⬇️
packages/strapi/lib/services/metrics/index.js	65.00% <0.00%> (-35.00%)	⬇️
...admin/admin/src/components/ContainerFluid/index.js	66.66% <0.00%> (-33.34%)	⬇️
...in-upload/admin/src/containers/HomePage/reducer.js	65.85% <0.00%> (-18.53%)	⬇️
... and 651 more

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[alexandrebodin]

LGTM, thanks for the update