[feature-request] Allow user to specify user agent in CLI options

[CrazySqueak]

Hello there, sorry if this isn't the right place to post this.

Rationale

Currently, the dump generator attempts to mimic a browser user agent.
In the MediaWiki API documentation, it is recommended that the user sets a custom, descriptive user agent identifying themselves, and especially discourages mimicking a browser user agent, as doing so could be misconstrued as malicious behaviour.

Currently, changing the user agent requires finding a specific function hidden in the code and editing it to replace the list of user agents. This is obtuse, and especially hard for a user to figure out when all they can tell is that they're getting HTTP 403 errors.

Proposed Feature

The user should be able to use a command-line argument to specify a custom user agent to be used instead. For example, passing the command-line argument
--user-agent="MyNameBot/1.2 ([email protected]) MediaWikiClientTools/3"
would then change the user agent to such.

[yzqzss]

patches:

saveweb@62f0c56
saveweb@fdc11f6
saveweb@8ac253f

[CrazySqueak]

That fork works like a charm. Thank you!

[robkam]

Please someone merge these into mediawiki-dump-generator.