Why this change?
Firstly, note that this is not a security commit because this feature is
still in development and should not be used anywhere.
The reason we want to set a limit here is to greatly reduce the
possibility of a DoS attack in the future via `ThemeSetting` where
someone would set an arbituary large json string in
`ThemeSetting#json_value` and causing the server to run out of resources
trying to serialize/deserialize the value.
What does this change do?
Adds an ActiveRecord validation to ensure that the bytesize of the json
string being stored is smaller than or equal to 0.5mb. We believe 0.5mb
is a decent limit for now but we can review the limit in the future if
we believe it is too small.
Why this change?
This commit introduces an experimental `type: objects` theme setting
which will allow theme developers to store a collection of objects as
JSON in the database. Currently, the feature is still in development and
this commit is simply setting up the ground work for us to introduce the
feature in smaller pieces.
What does this change do?
1. Adds a `json_value` column as `jsonb` data type to the `theme_settings` table.
2. Adds a `experimental_objects_type_for_theme_settings` site setting to
determine whether `ThemeSetting` records of with the `objects` data
type can be created.
3. Updates `ThemeSettingsManager` to support read/write access from the
`ThemeSettings#json_value` column.
