'any' type is supported starting from Go1.18. Let's consistently use it
instead of 'interface{}' type across the code base, since `any` is easier to read than 'interface{}'.
- Return meta-labels for the discovered targets via promutils.Labels
instead of map[string]string. This improves the speed of generating
meta-labels for discovered targets by up to 5x.
- Remove memory allocations in hot paths during ScrapeWork generation.
The ScrapeWork contains scrape settings for a single discovered target.
This improves the service discovery speed by up to 2x.
Previously ScrapeConfig.clone() was improperly copying promauth.Secret fields -
their contents was replaced with `<secret>` value.
This led to inability to use passwords and secrets in `-promscrape.config` file.
The bug has been introduced in v1.77.0 in the commit 67b10896d2
Updates https://github.com/VictoriaMetrics/VictoriaMetrics/issues/2551
* Add omitempty for DisableCompression and DisableKeepAlive fields in ScrapeConfig
* Add omitempty annotation to all the default/optional values
* Fix annotations after review
