lib/log: initial implementation

Created by: bobheadxi

Sets up an initial draft of the logging library, and what the implementation might look like. Closes https://github.com/sourcegraph/sourcegraph/issues/33953 , closes https://github.com/sourcegraph/sourcegraph/issues/33477, closes https://github.com/sourcegraph/sourcegraph/issues/33474 as part of https://github.com/sourcegraph/sourcegraph/issues/33192

• What this might look like in action: https://github.com/sourcegraph/sourcegraph/pull/34155
• Usage docs: see add_and_use_logging
• Main public APIs:
  • lib/log/logger.go
  • lib/log/init.go

Some core concepts:

1. Do not export directly usable log functions. We want to encourage users to hold their own references to loggers, so that fields can be attached. 2. Internally we still maintain a global logger with Resource information though, which tracks the current program.
2. Export a subset of Zap API. Hopefully, users of this package will never have to import zap directly. Whether or not that's a good idea yet... not sure, but I think it is - makes the API surface much smaller
   1. Related - we're only exporting the strongly typed logger implementation. Too verbose? Maybe, but I think this interface is better than the log15-like SugaredLogger, and in combination with restricted API avoids having giant objects be logged.
   2. If we're okay with this, it makes https://github.com/sourcegraph/sourcegraph/issues/33473 much easier, because we can just hook into the re-exported Field constructors
3. The standard logger tries its hardest to be OpenTelemtry-compliant https://opentelemetry.io/docs/reference/specification/logs/data-mode , and as such requires some slight hackery with zapAdapter
4. Desired (distant) end state: ban imports of log15, log, zap, etc. - all logging must handle by log.Scoped() and then using that

Prior art:

• https://sourcegraph.com/github.com/sourcegraph/sourcegraph/-/blob/internal/logging/main.go

Currently not in scope:

• Integrations with other observability packages and constructs https://github.com/sourcegraph/sourcegraph/issues/34217#issuecomment-1105357381
• Dynamic log levels (log levels are currently configured once on init) https://github.com/sourcegraph/sourcegraph/issues/33475

Test plan

unit tests and manual tests. this is mostly pretty self-contained at the moment