Introduce the LOTUS_CHAIN_BADGERSTORE_DISABLE_FSYNC envvar

[ribasushi]

This is a redux of #5050

Allows the user to control the opts.SyncWrites option of BadgerDs, with the tri-state environment variable LOTUS_CHAIN_BADGERSTORE_DISABLE_FSYNC

• unset == the default (currently fsync enabled)
• set with a false-y value ( "", "0", "no", "false" ) == fsync enabled no matter what a future default is
• set with any other value == fsync is disabled ignored defaults (recommended for day-to-day use)

Applying this brought @whyrusleeping's average chain validation times from "impossible to sync" ( > 30s ) down to 1~3s/tipset

[magik6k]

It would be nice if we could use the config for this.

(also should apply to the splitstore hotstore badger)

[ribasushi]

@magik6k there is opposition to this option on the team ( see previous issue ), so the suggested way forward was an undocumented envvar. I can certainly plumb this through the config, but I am not sure exposing this functionality is generally desired....

(also should apply to the splitstore hotstore badger)

@vyzo can you help with a pointer which spots should be covered? ( having a bit of trouble navigating through the new codebase )

[vyzo]

The spllitstore badger uses the fsrepo options constructor, so we should be covered by this.