PMM-14493 Document the default --log-driver of Podman

[ademidoff]

PMM-14493

This pull request updates the PMM Server installation documentation for Podman to clarify log driver compatibility and improve instructions for waiting on container startup. The main changes are a new warning about supported log drivers and a simplification to the startup wait command.

Documentation improvements:

• Added a warning explaining that the default log driver under systemd with Podman is journald, which is recommended, and that using --log-driver passthrough is not supported because it breaks PMM Server's nginx startup. The warning includes a description of the error message and lists supported log drivers.

Instruction simplification:

• Removed an unnecessary sleep 80 command from the container startup instructions, relying instead on timeout 60 podman wait --condition=running pmm-server to wait for the container to be ready.

[catalinaadam]

Doc review (Percona style guide)

The overall direction is good — the warning fills a real gap and the sleep 80 removal is a clean improvement. A few style suggestions below.

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1. Code block missing language specifier

The nginx error output block uses a bare fence with no language tag. Per our style guide, output blocks should use text:

```text
[emerg] open() "/dev/stderr" failed (6: No such device or address)
nginx: configuration file /etc/nginx/nginx.conf test failed
```

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2. Sentence fragment in the last line of the warning

Supported log drivers: journald (recommended — ...) and none (disables logging entirely).

This is a fragment. Rewrite as a full sentence:

The supported log drivers are journald (recommended — logs are persistent and visible via journalctl -u pmm-server) and none (disables logging entirely).

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3. Long sentence — consider splitting

Podman's passthrough driver passes the host's stdio file descriptors directly into the container, which makes /dev/stdin, /dev/stdout, and /dev/stderr unavailable inside the container.

The style guide asks for short sentences with a maximum of two clauses. This one is at the limit and is dense. Suggested split:

Podman's passthrough driver passes the host's stdio file descriptors directly into the container. This makes /dev/stdin, /dev/stdout, and /dev/stderr unavailable inside the container.

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4. Redundant bold on "not"

Do not use --log-driver passthrough.

The !!! warning admonition already signals importance. Bolding not inside it is redundant and goes against the style guide's preference for restraint in emphasis. Plain Do not use is sufficient.

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Minor positive notes

• Warning admonition syntax (!!! warning "Log driver compatibility") is correct.
• Code spans used correctly for flags, paths, and commands throughout.
• The missing newline at end of file fix is appreciated.