Refactor: Introduce BaseThirdPartyWiki

Backgroud

This is a NEW MR based on !74501 (closed), because original MR is out of date.

Depend on MR: !74140 (merged)

What does this MR do?

• Extract Shimo and Confluence public methods to BaseThirdPartyWiki

• Add restrictions: Only one third-party wiki service can be active at a time.

Migrations

bundle rake db:migrate:up VERSION=20220310072154

== 20220310072154 MigrateShimoConfluenceServiceCategory: migrating ============
== 20220310072154 MigrateShimoConfluenceServiceCategory: migrated (0.0320s) ===

bundle rake db:migrate:down VERSION=20220310072154

== 20220310072154 MigrateShimoConfluenceServiceCategory: reverting ============
== 20220310072154 MigrateShimoConfluenceServiceCategory: reverted (0.0120s) ===

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