Configuration page rework: remove duplication, make easier to maintain, add missing flag

[chalin]

The Configuration pages for v3.5 and v.34 combined get ~2% traffic relative to the overall site: my guess is that most users simply run etcd -h.

This PR:

• Reworks and simplifies the 3.5 Configuration page to, in particular, remove duplication and make it easier to maintain.
• For now, I've opted to show the configuration flags as they're output by the etcd -h command, which make maintenance much easier.
• Addresses Add doc for --initial-election-tick-advance flag #433 for the v3.5 page
• Also removes obsolete flags.

Later we could consider writing a shortcode to format the command-line flag information more nicely.

Preview: https://deploy-preview-491--etcd.netlify.app/docs/v3.5/op-guide/configuration/

[chalin]

Update: in order to preserve the ability to link into flag sections, I've split the etcd -h output into markdown sections (manually, ideally we'll like to get a shortcode and/or script to do this -- but that'll be for later).

[nate-double-u]

I like this organization @chalin, thanks for this.

I've put one nit inline regarding spacing. Otherwise, /lgtm

[chalin]

Thanks for the review, and the suggested change (which I've accepted).

[chalin]

@spzala - WDYT?

[spzala]

Have one inline comment but other than that lgtm
Thanks @chalin @nate-double-u

[spzala]

Can we keep it just "Proxy" instead of v2 Proxy.. (similar to how it's originally mentioned ## Proxy flags) Thanks!

[chalin]

As I mentioned in the opening comment:

• I've opted to show the configuration flags as they're output by the etcd -h command, which make maintenance much easier.

The "v2 Proxy" comes from the command's help text. I'd rather match the help text (given that we're aiming to have this page generated automatically from the help text), but if you feel strongly about it I can make the change. Please let me know. Thanks.

[chalin]

Actually, @spzala, I'll let you answer here. Thanks.

Maybe we should open an issue an issue over the etcd repo to have the flag group title changes?

[chalin]

I'm going to merge based on @spzala's LGTM in #491 (review), and then open a followup issue for #491 (comment).