box: disallow granting execute privilege on space

Closes #9277

@TarantoolBot document
Title: Document `box_space_execute_priv` compatibility option

Historically, it was possible to grant the `execte` privilege on
a space although this action had no effect. Since Tarantool 3.0
it isn't allowed anymore. The new `compat` module option
`box_space_execute_priv` was added to revert to the old behavior.

Please create a documentation page for the new compatibility option at
https://tarantool.io/compat/box_space_execute_priv

Example:

```
tarantool> box.cfg{log_level = 'error'}
---
...

tarantool> box.schema.user.create('alice')
---
...

tarantool> box.schema.user.grant('alice', 'execute', 'space')
---
- error: Unsupported space privilege 'execute'
...

tarantool> require('compat').box_space_execute_priv = 'old'
---
...

tarantool> box.schema.user.grant('alice', 'execute', 'space')
---
...
```