Fix crash when ansible_default_ipv4.address is undefined (PE-1998)

[mazam32-itential]

Summary

• redis_bind and redis_sentinel_bind (in roles/redis/defaults/main/redis.yml and roles/redis/defaults/main/sentinel.yml) assumed ansible_default_ipv4.address always exists.
• On hosts with no default route, Ansible sets ansible_default_ipv4 to an empty dict, so accessing .address raised AnsibleUndefinedVariable and aborted the entire run.
• Both variables now check ansible_default_ipv4.address is defined first, falling back to binding on 127.0.0.1 only when it's not present.
• All other references to this fact in the codebase (the three *-validation-report.md.j2 templates) already guarded with | default('N/A') and needed no changes.

How this was tested

1. Reproduced the crash with an ad-hoc Ansible command that simulates the "no default route" case (empty ansible_default_ipv4 fact), using the exact pre-fix expression:

   ansible localhost -m debug -a "msg={{ '127.0.0.1 ' ~ ansible_default_ipv4.address }}" -e '{"ansible_default_ipv4": {}}'

   Result: FAILED! => "'dict object' has no attribute 'address'" — confirming the exact failure mode described in the ticket.

2. Verified the fix by running the same style of check against the new expression, for both the broken case and the normal case:

   # Undefined case — should not crash, should fall back to 127.0.0.1 only
   ansible localhost -m debug -a "msg={{ '127.0.0.1' ~ ((' ' + ansible_default_ipv4.address) if (ansible_default_ipv4.address is defined) else '') }}" -e '{"ansible_default_ipv4": {}}'
   # => SUCCESS, msg: "127.0.0.1"
   
   # Normal case — address present, should still be appended (no regression)
   ansible localhost -m debug -a "msg={{ '127.0.0.1' ~ ((' ' + ansible_default_ipv4.address) if (ansible_default_ipv4.address is defined) else '') }}" -e '{"ansible_default_ipv4": {"address": "10.0.0.5"}}'
   # => SUCCESS, msg: "127.0.0.1 10.0.0.5"

3. Confirmed the YAML still parses to the identical single-line Jinja expression after wrapping it across two lines for line-length (folded scalar >-), using PyYAML to load both files and print the resulting redis_bind/redis_sentinel_bind values.

4. Ran ansible-lint against both changed files — passes clean (0 failures, 0 warnings):

   ansible-lint roles/redis/defaults/main/redis.yml roles/redis/defaults/main/sentinel.yml

5. End-to-end sanity check: this same Redis role (unmodified logic aside from this fix) was used minutes earlier in a full itential.deployer.site run against a live EC2 instance (Rocky Linux 8, AIO topology) where ansible_default_ipv4.address was defined — Redis, Sentinel, MongoDB, Platform, and Gateway all installed and started successfully, confirming this change doesn't alter behavior on hosts where the fact is present.

Test plan for reviewer

• Confirm the two diffs only touch the redis_bind/redis_sentinel_bind default definitions
• Re-run the ad-hoc ansible localhost -m debug commands above to reproduce/verify locally
• Optionally run itential.deployer.redis against a host with no default route to confirm no crash end-to-end