startami: strip trailing '})' from amicmd to avoid eval syntax error

[laurentroque]

Description

Strip trailing config-artifact characters (e.g., })) from the amicmd string constructed in scripts/startami before it is executed.

Motivation and Context

startami -c cxi_0.cnf could fail with:
eval: syntax error near unexpected token ')'

On CXI hosts, amicmd was being parsed from the ami_client line in cxi_0.cnf and could end up with a trailing }), causing bash eval to error. This change sanitizes the constructed command to avoid the syntax error.

How Has This Been Tested?

• cxi-monitor: /cds/home/i/iroque/programs/engineering_tools/scripts/startami -c cxi_0.cnf (reaches expected restart prompt; no eval syntax error)
• cxi-control: /cds/home/i/iroque/programs/engineering_tools/scripts/startami -c cxi_0.cnf (successfully launches online_ami; no eval syntax error)
• xcs-control: /cds/home/i/iroque/programs/engineering_tools/scripts/startami (successfully launches online_ami; no eval syntax error)

Where Has This Been Documented?

• Inline comment added next to the new amicmd sanitisation line in scripts/startami.
• Jira ticket: ECS-9707

[ZLLentz]

Some nitpicky questions, if this works I think it's correct to merge without addressing these.
I'm mostly trying to update my own sed/regex knowledge.

• Why is this a new command using printf instead of joining onto the | sed train on line 74?
• (Conversely, if new commands are preferred for readability, maybe we should unwrap more of them)
• Why printf with no formatting over echo?
• What's [[:space:]]* doing in the sed here? Are you expecting e.g. })? Your PR description only mentions })
• It looks like you're using a literal [})] followed by a [})]*, but in regex we have a + operator for matching 1 or more instances of a symbol. This could have been [})]\+