[7.x] [kbn/std] add observable helpers to aid with rxjs 7 upgrade (#79752)

[spalger]

Backports the following commits to 7.x:

• [kbn/std] add observable helpers to aid with rxjs 7 upgrade ([kbn/std] add observable helpers to aid with rxjs 7 upgrade #79752)

[kibanamachine]

💚 Build Succeeded

• continuous-integration/kibana-ci/pull-request
• Commit: 9bc1505

Metrics [docs]

@kbn/optimizer bundle module count

id	before	after	diff
core	440	441	+1
data	571	572	+1
graph	169	170	+1
ingestManager	548	549	+1
uiActionsEnhanced	138	139	+1
total			+5

async chunks size

id	before	after	diff
data	273.8KB	274.7KB	+944.0B
graph	1.3MB	1.3MB	+945.0B
ingestManager	1.2MB	1.2MB	+944.0B
total			+2.8KB

distributable file count

id	before	after	diff
default	48760	48761	+1
oss	29467	29468	+1

page load bundle size

id	before	after	diff
core	652.4KB	653.3KB	+938.0B
data	1.1MB	1.1MB	+65.0B
graph	16.1KB	16.2KB	+65.0B
uiActionsEnhanced	327.0KB	327.9KB	+1005.0B
total			+2.0KB

To update your PR or re-run it, just comment with:
@elasticmachine merge upstream