compose: Use service tokens for fleet-server

[marclop]

Motivation/summary

This patch updates the current fleet-server container to use a custom
entrypoint which creates a service token and uses it. This is necessary
since support to authenticate against Elasticsearch using username /
password authentication has been removed from 8.0 onwards.

Additionally, the docker-compose file has been updated to wait for the
fleet-server container to be healthy before exiting.

Checklist

N/A

[apmmachine]

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Build stats

• Start Time: 2022-01-10T09:53:25.655+0000

• Duration: 42 min 42 sec

• Commit: b973381

Test stats 🧪

Test	Results
Failed	0
Passed	5624
Skipped	20
Total	5644

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[simitt]

/test

[marclop]

The TBS system test is failing due to elastic/fleet-server#1048

[marclop]

There's a pending change on the Elastic Agent that would allow us to continue using user/password in the container, the Elastic Agent itself would generate the service token and pass it down: elastic/beats#29651

[simitt]

@marclop the linked PR in beats has been merged. My understanding is that the container setup still needs to use username+password for the setup to be able to receive a service token with correct privileges. Is this change here needed then?

[marclop]

@simitt We are good to close, thanks for the ping.