feat(lib): allow to add custom storage

[va-stefanek]

PR Checklist

Please check if your PR fulfills the following requirements:

• [X] The commit message follows our guidelines: https://github.com/ngneat/forms-manager/blob/master/CONTRIBUTING.md#commit
• [ ] Tests for the changes have been added (for bug fixes / features)
• [X] Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

[ ] Bugfix
[X] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[ ] Documentation content changes
[ ] Other... Please describe:

What is the current behavior?

Currently we can only use localStorage as a persistence storage

Issue Number: #6

What is the new behavior?

We can use any persistence storage which extends proper interface

Does this PR introduce a breaking change?

[ ] Yes
[ ] No

Other information

[NetanelBasal]

Thanks for the PR. Can you update the docs, please?

[va-stefanek]

@NetanelBasal Done.

[AdmilsonCossa]

Any updates on this feature? This is very important!

[va-stefanek]

@AdmilsonCossa I will try to complete this by the end of the week.

[hiepxanh]

@va-stefanek looking for your update sir :D

[va-stefanek]

@NetanelBasal let me know if we are still interested in that feature, whether we should remove FORMS_MANAGER_SESSION_STORAGE_PROVIDER. I have pushed new changes with using @ngneat/storage

Sorry everyone for the delay.

[hiepxanh]

ya I'm looking for this feature still waiting :D

[NetanelBasal]

@va-stefanek sure