feat: implement com.redhat.rhsm.content Varlink interface

[DuckBoss]

Add the Refresh(force, metadata) method to a new com.redhat.rhsm.testing.content Varlink interface. It refreshes the installed SCA entitlement certificate (optionally forcing a fresh fetch) and regenerates redhat.repo accordingly, per the rhsm-varlink design doc. Business logic lives in rhsm2's UpdateEntitlementCertificate and GenerateRepoFileFromInstalledEntitlementCerts; this wires it into the same Backend/Handler pattern already used by the override and release interfaces.

Blocked by:

• fix: don't delete entitlement cert when reissued with the same serial jirihnidek/rhsm2#109
• feat: support forced entitlement cert refresh and export repo generation jirihnidek/rhsm2#106
  • go.mod currently pins that branch's commit and needs bumping to a rhsm2 main commit once that PR lands.

Resolves: CCT-1716

1. Environment:

$ testing-farm reserve --compose RHEL-10.3-Nightly
$ git clone https://github.com/RedHatInsights/rhc.git && cd rhc/
$ git checkout jajerome/cct-1716-content-varlink-interface
$ make build

2. Start rhc-server:

$ ./rhc-server &

3. Confirm the interface is registered:
   Look for com.redhat.rhsm.testing.content in the interface list.

$ varlinkctl info /run/rhc/com.redhat.rhc

4. Error path: unregistered system (no registration needed for this one)

$ varlinkctl call --json=short /run/rhc/com.redhat.rhc \
  com.redhat.rhsm.testing.content.Refresh '{"force": false}'
# error: com.redhat.rhsm.testing.content.SystemNotRegistered

5. Register, then demo a regular Refresh:

$ ./rhc connect --username <user> --password <pass> --organization <org> \
  --enable-feature content --disable-feature analytics --disable-feature remote-management
$ ./rhc status --format json | jq   # confirm rhsm_connected: true
$ ls -la /etc/pki/entitlement/                 # note serial + mtime

Run the refresh method: entitlement cert serial/mtime unchanged (conditional If-Modified-Since GET → 304).

$ varlinkctl call --json=short /run/rhc/com.redhat.rhc \
  com.redhat.rhsm.testing.content.Refresh '{"force": false}' | jq
#  {"success": true}

6. Force refresh: round trip proving the cert actually updates

$ varlinkctl call --json=short /run/rhc/com.redhat.rhc \
  com.redhat.rhsm.testing.content.Refresh '{"force": true}' | jq
# {"success": true}
$ ls -la /etc/pki/entitlement/     # fresh fetch: If-Modified-Since is skipped with force=true
$ cat /etc/yum.repos.d/redhat.repo

7. Idempotency: run the refresh multiple times
   Both return {"success": true}, no crash, no duplicate files left in /etc/pki/entitlement/.

$ varlinkctl call --json=short /run/rhc/com.redhat.rhc \
  com.redhat.rhsm.testing.content.Refresh '{"force": false}' | jq
$ varlinkctl call --json=short /run/rhc/com.redhat.rhc \
  com.redhat.rhsm.testing.content.Refresh '{"force": false}' | jq

[cnsnyder]

LGTM! Thank you!