docs: add specification of executor and flow yaml

[JohannesMessner]

TODO:

• mention environment variables and internal links

[github-actions]

Latency summary

Current PR yields:

• 😶 index QPS at 1323, delta to last 2 avg.: +2%
• 😶 query QPS at 71, delta to last 2 avg.: +0%
• 🐎🐎 avg flow time within 1.5263 seconds, delta to last 2 avg.: +6%
• 😶 import jina within 0.4819 seconds, delta to last 2 avg.: +0%

Breakdown

Version	Index QPS	Query QPS	Avg Flow Time (s)	Import Time (s)
current	1323	71	1.5263	0.4819
3.4.4	1386	77	1.5665	0.4443
3.4.3	1196	65	1.3025	0.5194

Backed by latency-tracking. Further commits will update this comment.

[JohannesMessner]

This patterns does not seem to work. But also not sure if we even want to promote it. Reason: People should probably have yaml files for their executors anyways, and those would include py_modules already.

[JoanFM]

then remove if it does not seem to work

[github-actions]

📝 Docs are deployed on https://docs-yaml-spec--jina-docs.netlify.app 🎉