add mail template command

[VoigtS]

Includes the mail-template command which can be used to view the stringified or JSON escaped content of all templates or an individual template.

[Copilot]

Pull request overview

Adds a new CLI surface to inspect rendered mail templates returned by the Limes admin API, to help validate template configuration.

Changes:

• Introduce cluster mail-template command with subcommands to print all templates or individual templates.
• Add a --json output flag for the mail-template subcommands.
• Wire the new command into the existing cluster command tree.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
internal/cmd/mail_template.go	Implements mail-template command, fetching templates from admin/mail/render and printing them (raw or JSON).
internal/cmd/flags.go	Adds mailTemplateFlags with a --json boolean.
internal/cmd/cluster.go	Registers the new mail-template command under cluster.

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[github-actions]

Merging this branch will not change overall coverage

Impacted Packages	Coverage Δ	🤖
github.com/sapcc/limesctl/internal/cmd	0.00% (ø)

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Coverage by file

Changed files (no unit tests)

Changed File	Coverage Δ	Total	Covered	Missed	🤖
github.com/sapcc/limesctl/internal/cmd/cluster.go	0.00% (ø)	0	0	0
github.com/sapcc/limesctl/internal/cmd/mail_template.go	0.00% (ø)	0	0	0

Please note that the "Total", "Covered", and "Missed" counts above refer to code statements instead of lines of code. The value in brackets refers to the test coverage of that file in the old version of the code.