Restrict length of exception messages

[basepi]

What does this pull request do?

Restricts the length of the message field for exceptions captured by the agent. Continuation of the theme in #305.

Related issues

Closes #1614

[apmmachine]

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• Start Time: 2022-08-18T22:42:32.026+0000

• Duration: 30 min 4 sec

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Test	Results
Failed	0
Passed	4974
Skipped	3420
Total	8394

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🌐 Coverage report

Name	Metrics % (covered/total)	Diff
Packages	100.0% (68/68)	💚
Files	100.0% (227/227)	💚
Classes	100.0% (227/227)	💚
Lines	89.755% (17452/19444)	👍 0.004
Conditionals	77.18% (3186/4128)	👍

[trentm]

LGTM.