Flowable IDM UI fails to jump to the root web context.

**Problem describe**
The UI works well if a root web context like '/flowable-ui' is used.
If the root web context is '/' or '', the idm UI fails to jump to the root web context.(On the IDM UI page, click the 'flowable' icon in the upper left corner)

**Expected**
the idm UI should jump to the root web context.(On the IDM UI page, click the 'flowable' icon in the upper left corner)

**Code**
Seems to me the issue is caused by the following code part in app-cfg.js:
`var pathname = window.location.pathname.replace(/^(\/[^\/]*)(\/.*)?idm\/?$/, '$1').replace(/\/$/, '');`

Operated on a '/flowable-ui' root web context the value of pathname will always be '/flowable-ui'. Jump function work well.
Operated on a '/' root web context the value of pathname will always be ''. Jump function does not meet expectations.

Case: when the root web context is '/' or ''
In the idm app ui, the `window.location.pathname` like this '/idm/'.
The value of pathname will always be ''. Jump logic is actually `window.location.href = pathname`, so the page will always stay on 'http://ip:port/idm/'. The expected result is to jump to 'http://ip:port/'.

**Additional context**
my pom.xml
```xml

4.0.0

org.springframework.boot
spring-boot-starter-parent
2.2.2.RELEASE


org.example
FlowableBoot
1.0-SNAPSHOT

1.8
6.6.0

org.flowable
flowable-spring-boot-starter-rest
${flowable.version}


org.flowable
flowable-spring-boot-starter-ui-idm
${flowable.version}


org.flowable
flowable-spring-boot-starter-ui-modeler
${flowable.version}


org.flowable
flowable-spring-boot-starter-ui-admin
${flowable.version}


org.flowable
flowable-spring-boot-starter-ui-task
${flowable.version}

mysql
mysql-connector-java
runtime

org.springframework.boot
spring-boot-maven-plugin

```

Beginne in app-cfg.js, wo die IDM UI pathname aus window.location.pathname ableitet und sie window.location.href zuweist, wenn auf das Flowable-Symbol geklickt wird. Reproduziere das Verhalten, wenn die IDM UI unter '/' oder '' sowie unter '/flowable-ui' eingebunden ist. Als erledigt gilt, dass das Symbol in beiden Fällen zum Root-Webkontext navigiert, ohne den Nicht-Root-Kontext zu beeinträchtigen.

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