Add OpenBao Monitoring

[technowhizz]

To be merged after stackhpc/ansible-collection-hashicorp#93 merges and then bumping the requirements.yml for the collection

[gemini-code-assist]

Code Review

This pull request introduces monitoring support for OpenBao, including Prometheus scrape configurations, alerting rules for sealed or unhealthy nodes, and corresponding documentation. A critical issue was identified in the Prometheus scrape configuration template, where the Kayobe-specific inventory group 'controllers' and filter 'net_ip' were used instead of Kolla-native equivalents ('control' group and 'kolla_address' filter), which would cause template rendering failures.

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[technowhizz]

Hmm CI is failing because the prometheus scrape job is enabled by default (assuming most clients have openbao deployed) but because we manually have to deploy openbao, it's not set up in the CI and so there is a prometheus alert for exporter down.

Should we have it disabled by default and get the deploy openbao playbook to change some var to enable it?

@jovial @dougszumski What do you think?