The following regex patterns are optimized:
- literal string match, e.g. "foo"
- prefix match, e.g. "foo.*" and "foo.+"
- substring match, e.g. ".*foo.*" and ".+foo.+"
- alternate values match, e.g. "foo|bar|baz"
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
