Extend configuration to set maximum claim size

[letmaik]

Currently, an upper limit of 1 MiB is hard-coded. This should be configurable, defaulting to 1 MiB.

Generally, the idea is still that the ledger should not contain large content, so setting this to 1 GiB or similar is discouraged. The solution to this is to reference content stored elsewhere (by hash) instead of embedding it.

[ivarprudnikov]

• Reference to our hardcoded value https://github.com/microsoft/scitt-ccf-ledger/blob/main/app/src/constants.h#L14
• Reference to the default limit in CCF https://github.com/microsoft/CCF/blob/main/include/ccf/http_configuration.h#L14
• Reference to CCF doc https://microsoft.github.io/CCF/main/operations/generated_config.html#http-configuration