Improve filenames creation for Snowplow event definitions generator

What does this MR do and why?

• Prefix the generated filename with a timestamp
• Remove special characters when concatenating the category and action into the filename.
• Make sure filenames length is lower than 100 characters (related).

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How to set up and validate locally

1. Run Gitlab::SnowplowEventDefinitionGenerator.new([], {category: "YOUR CAT NAME", action: "YOUR ACTION NAME"}).invoke_all
2. Check generated file name

For example:

[9] pry(main)> Gitlab::SnowplowEventDefinitionGenerator.new([], {category: "YOUR%% CAT NAME", action: "YOUR::A$!$CTION NAME"}).invoke_all
      create  config/events/1642996243_yourcatname_your__actionname.yml

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #341062 (closed)