No longer allow overriding the frozen attribute of containers

[julianbrost]

The Array, Dictionary, and Namespace types provide a Freeze() method that makes them read-only. So far, there was the possibility to call some methods with overrideFrozen=true which would then bypass the corresponding check and allow modification of the data structures nonetheless.

With #9627 (24b57f0), this possibility was already removed from the Namespace type. However, for interface compatibility, it kept the parameter and just ignores it, throwing an exception on any modification on a frozen instance.

The only place using overrideFrozen was processing of the -D/--define command line flag that allows setting additional variables in the DSL. At the time it is evaluated, there are no user-created data structures yet that could be frozen, so the only frozen objects that could be encountered are Namespaces (Icinga doesn't freeze other types by itself) and for these, overrideFrozen already has no effect.

Hence, there is no harm in removing overrideFrozen altogether. This simplifies the code and also means that frozen objects are now indeed read-only without exceptions, allowing further optimizations regarding locking in the future. In particular, #10414 currently assumes that frozen Arrays/Dictionaries can be iterated without holding (which is only true as long as there is no operation with overrideFrozen).

Tests

Because of the following, I don't expect any observable difference in behavior from this change:

The only place using overrideFrozen was processing of the -D/--define command line flag that allows setting additional variables in the DSL. At the time it is evaluated, there are no user-created data structures yet that could be frozen, so the only frozen objects that could be encountered are Namespaces (Icinga doesn't freeze other types by itself) and for these, overrideFrozen already has no effect.

I've tested that Icinga 2 still starts with this changes and works in general. Additionally, I've also successfully tested a config deployment from Director (as that's a case that makes use of --define).

[yhabteab]

$ grep --exclude-dir=build --exclude-dir=prefix --exclude-dir=doc -niR 'overrideFrozen' .
<nothing>

Config package updates (director):

...
[2025-07-08 15:37:18 +0200] information/ApiListener: New client connection from [::1]:52531 (no client certificate)
[2025-07-08 15:37:18 +0200] information/ConfigPackageUtility: Updating configuration file: /Users/yhabteab/Workspace/icinga2/prefix/var/lib/icinga2/api/packages/example-cmdb/dc8d5503-71a4-4498-9c8b-637e99bd06c1/conf.d/test.conf
[2025-07-08 15:37:18 +0200] information/HttpServerConnection: Request POST /v1/config/stages/example-cmdb (from [::1]:52531, user: root, agent: curl/8.7.1, status: OK) took total 1ms.
[2025-07-08 15:37:18 +0200] information/HttpServerConnection: HTTP client disconnected (from [::1]:52531)
[2025-07-08 15:37:20 +0200] information/Application: Got reload command: Starting new instance.
...