[IMP] Email marketing: Analyze metrics reports

[pabr-odoo]

Task card: https://www.odoo.com/odoo/project/3835/tasks/4112632

Overhauling the analyze metrics doc to refocus on specific use cases rather than just definitions and contain information on generating different types of reports using the analysis dashboard.

[robodoo]

[pabr-odoo]

Hey @ksc-odoo have an improvement ready for first review from you whenever you get the chance. Thanks!

[pabr-odoo]

Hey @StraubCreative this improvement is ready for your final review whenever you get the chance. Thanks!

[pabr-odoo]

Hey @samueljlieber this PR is ready for tech review whenever you get the chance. Thanks!

[pabr-odoo]

@robodoo r+

[StraubCreative]

This PR's merge function appears to have malfunctioned?

Clean rebase on 331f11a (no conflicts). ... @robodoo r+

[robodoo]

@pabr-odoo @StraubCreative staging failed: ci/runbot on c84f8109a757db45836908c293ae96693fab823d (view more at https://runbot.odoo.com/runbot/build/70904770)

[samueljlieber]

@robodoo retry

[robodoo]

@pabr-odoo @StraubCreative staging failed: ci/runbot on 146d2f50e5cccfcfca1c84ab6849cbdc4038d814 (view more at https://runbot.odoo.com/runbot/build/70973818)

[samueljlieber]

@robodoo retry