refactor!: environment variables validation

[AlexanderLukin]

Refactor environment variable validation rules. Apply consistent patterns to env validation.

The main motivation for this change was as follows:

1. Make env validation more strict and consistent. Stick to the same validation patterns in different projects.

2. Provide consistent fallback options for optional variables.

Here are the main changes:

1. Previously if a user set an empty string as the variable name in the .env file like this: VARIABLE_NAME= not all variable initializers assigned a correct default value to the variable in this case. Now it is fixed. For the purpose of this improvement, now all optional variable initializers always have the @Transform decorator that provides a default value for the variable. Add the two special functions (toNumber and toBoolean) that support this change.

2. Make validation of boolean variables more strict.
   CAUTION: This might be a breaking change for users who use values like "yes" to initialize boolean variables.

3. Now the ETH_NETWORK variable is validated not only when the validator source is "Lido". Make validation of this variable more strict.
   CAUTION: Currently the EVM doesn't officially support testnets other than those listed in the Network interface. But this might be a breaking change if some users use EVM for other testnets.

4. Implement the new toArrayOfUrls() function to provide a reasonable default value for variables that should have a list of URLs in their values. This function also fixes a bug with default values for such variables. Previously, if a user set an empty string as a value of such variables, the validation worked incorrectly.

5. Now we validate that values in EL_RPC_URLS, CL_API_URLS, and VALIDATOR_REGISTRY_KEYSAPI_SOURCE_URLS are indeed URLs.

6. The validation engine now removes trailing slashes from URL values.

7. More consistent validation for the HTTP_PORT and DB_PORT values.

8. Add @Optional decorator to all optional variables.

9. Change @IsNumber to @IsInt.

10. Move enums from the env.validation.ts to environment.interface.ts.

[AlexanderLukin]

Update validation rules for some variables. The main changes are:

1. Loosen validation rules for boolean variables. Now numbers "1" and "0" and constants "yes" and "no" are accepted as valid boolean values.

2. Rename the Network interface to Chain.