Add signals middleware

[silesky]

• Allow registration of middleware to allow for dropping and modification of signals
• Refactor to use middleware for network filter, rather than having that logic live in the network generator.

class MyMiddleware implements SignalsMiddleware {
 load(ctx: SignalsMiddlewareContext) {
   // this will block any signals from being emitted until resolved, like a segment 'before' plugin -- it will be invoked before processSignal
   // we can access ctx.unstableGlobalSettings from inside this plugin and assign it to the instance if needed
    return 
 }
  process(signal: Signal) {
    if (
      signal.type === 'network' &&
      signal.data.action === 'request' &&
      ...
    ) {
      // null = drop signal
      return null
    } else {
      return signal
    }
  }
}
const signalsPlugin = new SignalsPlugin({
  middleware: [new MyMiddleware()]
})

[changeset-bot]

🦋 Changeset detected

Latest commit: 90b27f6

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@segment/analytics-signals	Minor

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[codecov]

Codecov Report

Attention: Patch coverage is 66.12903% with 21 lines in your changes missing coverage. Please review.

Project coverage is 83.52%. Comparing base (3e8d9d2) to head (90b27f6).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
...e/network-signals-filter/network-signals-filter.ts	50.00%	8 Missing ⚠️
packages/signals/signals/src/core/emitter/index.ts	73.07%	7 Missing ⚠️
packages/signals/signals/src/lib/logger/index.ts	20.00%	4 Missing ⚠️
...ckages/signals/signals/src/core/signals/signals.ts	66.66%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1220      +/-   ##
==========================================
- Coverage   83.85%   83.52%   -0.33%     
==========================================
  Files         217      217              
  Lines        5798     5810      +12     
  Branches     1315     1324       +9     
==========================================
- Hits         4862     4853       -9     
- Misses        936      957      +21     

Flag	Coverage Δ
browser	92.22% <ø> (ø)
core	89.86% <ø> (ø)
node	87.93% <ø> (ø)

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.