network_traffic: add mappings for process.* fields

[efd6]

What does this PR do?

Adds mappings for process.* fields at the root level.

Checklist

• I have reviewed tips for building integrations and this pull request is aligned with them.
• I have verified that all data streams collect metrics or logs.
• I have added an entry to my package's changelog.yml file.
• I have verified that Kibana version constraints are current according to guidelines.

Author's Checklist

• I have added the fields to all the data streams and not just the 4 that were noted in the issue since the beat field.yml includes process.* in the common set.

How to test this PR locally

Related issues

• Closes [network_traffic] process.start is missing from mappings #3512

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• Start Time: 2022-06-29T00:36:54.944+0000

• Duration: 73 min 2 sec

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Passed	264
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Name	Metrics % (covered/total)	Diff
Packages	100.0% (0/0)	💚
Files	100.0% (0/0)	💚 3.401
Classes	100.0% (0/0)	💚 3.401
Methods	71.875% (46/64)	👎 -16.987
Lines	100.0% (0/0)	💚 10.053
Conditionals	100.0% (0/0)	💚

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Pinging @elastic/security-external-integrations (Team:Security-External Integrations)

[efd6]

It would be nice if process.* could be placed on server and client according to ECS.