Support Weblate Flags in Gettext Files via Extracted Comments

### Describe the problem

We use GNU gettext for translating strings for embedded systems, with our programmers providing human-readable cues for things like maximum character length via the extracted comments feature (example below).

```po
#.
#. STARTUP TYPEWRITER TEXT
#. ------------------------------------------------------------------
#. EEPROM BLANK (Maxlen=12)
msgid "BLANK"
msgstr "VIDE"

#. (DO NOT TRANSLATE!)
msgid "EEPROM"
msgstr ""
```

For our use case, this could potentially be a far more efficient means of setting [weblate-flags](https://docs.weblate.org/en/latest/admin/checks.html) such as `max-length:N` than manually setting said flags via Weblate's UI. Presently, however, only certain XML based formats support storage and synchronisation of [weblate-flags](https://docs.weblate.org/en/latest/admin/checks.html).

### Describe the solution you would like

We suggest supporting storage and synchronisation of [weblate-flags](https://docs.weblate.org/en/latest/admin/checks.html) within gettext's extracted comments, in a similar vain to the [non-standard weblate-flags attribute supported for XLIFF](https://docs.weblate.org/en/latest/formats/xliff.html#xliff-flags).

As the extracted comments feature of GNU gettext is designed to allow programmers to provide cues to translators, this would seem the ideal means of conveying machine-readable instructions to a translation tool such as Weblate.

### Example:
```po
#.
#. STARTUP TYPEWRITER TEXT
#. ------------------------------------------------------------------
#. EEPROM BLANK weblate-flags="max-length:12, priority:50"
msgid "BLANK"
msgstr "VIDE"

#. weblate-flags="read-only"
msgid "EEPROM"
msgstr ""

```

In the example above, [weblate-flags](https://docs.weblate.org/en/latest/admin/checks.html) are:

1. Appended to the end of the extracted comments.
2. Signified via the keyword/prefix `weblate-flags=`.
3. Encapsulated by double quotes.
4. Comma-delimited.

These would seem like reasonable conventions to follow?

### Describe alternatives you have considered

_No response_

### Screenshots

_No response_

### Additional context

_No response_