caddyhttp: Add server options keepalive_idle and keepalive_count

[joshuamcbeth]

This pull request adds keepalive_idle and keepalive_count per follow-up discussion in #7144.

Assistance Disclosure

No AI was used.

[joshuamcbeth]

Upon further review of the recent change history and discussion I think this should also have a keepalive_enable bool parameter so all struct fields directly map and all behaviors are supported.

[joshuamcbeth]

Actually, I guess it should be keepalive_disable if the default behavior should be enable.

This is reflected in the latest revision of the PR.

[francislavoie]

I'm not sure I like that "disabled" is a separate option because this would be a breaking change for anyone already doing interval -1 to disable. I think that behaviour should be retained at least.

[joshuamcbeth]

Fair enough.

I've reverted the keepalive_disable option and restored the keepalive_interval behavior for negative values.

Since negative values for the count and idle parameters never had any other meaning, I've preserved the "underlying socket value unchanged" for negative values there for now.

[francislavoie]

Thanks! I think some .caddyfiletest tests would be nice (or update an existing one)

[joshuamcbeth]

I updated the existing global_server_options_single.caddyfiletest to include the keepalive parameters.

[francislavoie]

Thanks!