RANGER-5475: Add support to fetch JWT if available in RangerRESTClient

[kumaab]

What changes were proposed in this pull request?

Update RangerRESTClient to support passing JWT if available while making calls.

Also, update callers: services tagsync and usersync.

JWT can be fetched from either of the below sources:

• env variable
• file
• credential file

How was this patch tested?

Following log is seen in both tagsync and usersync:

30 Jan 2026 23:43:27  INFO o.a.r.p.u.RangerRESTClient [main] - 776 Registering JWT auth header in REST client

using these configs for tagsync :

<property>
        <name>ranger.tagsync.policy.rest.client.jwt.source</name>
        <value>env</value>
</property>
<property>
        <name>ranger.tagsync.policy.rest.client.jwt.env</name>
        <value>JWT_ENV</value>
</property>

and these configs for usersync:

<property>
        <name>ranger.usersync.policy.rest.client.jwt.source</name>
        <value>file</value>
</property>
<property>
        <name>ranger.usersync.policy.rest.client.jwt.file</name>
        <value>/opt/ranger/usersync/conf/jwtFile</value>
</property>